US 7410246

US Patent 7,410,246 (US7410246B2) — Summary

Bibliographic data (from the authoritative patent text supplied and USPTO/Google Patents records)

Abstract (condensed)

A heater chip has a plurality of heaters each having a length, width, and thickness. Length × width (heater area) is in a range of about 50 to about 500 micrometers squared; thickness is in a range of about 500 to about 5000 or 6000 angstroms. Energy to jet a single ink drop is in a range of about 0.007 to about 0.99 or 1.19 microjoules. The chip is formed as thin-film layers on a substrate. Energy ranges are disclosed for all heaters having areas from about 50 to about 4000 μm² and thicknesses from about 500 to about 16,000 Å. Printheads and printers containing the chip are also disclosed.

Technology in plain language

The patent claims a thermal inkjet "heater chip" (the silicon die containing the tiny resistive heaters that boil ink to eject drops). The invention is essentially a dimensional/energy recipe: for a given heater footprint (length × width) and heater thickness, the specification teaches the firing energy needed to achieve stable bubble nucleation and drop ejection. It discloses that stable jetting occurs when heater power per unit volume exceeds about 1.5 × 10¹⁵ W/m³ and provides tables (Figs. 10–12) mapping heater area and thickness to preferred per-drop energy ranges. The claimed structure is the standard thin-film stack: substrate → thermal barrier layer → resistor layer (its width defines the heater width) → conductor layer (anode/cathode spacing defines the heater length) → overcoat (passivation, optionally plus cavitation layer); combined overcoat + resistor thickness defines the heater thickness.

Plain-language overview of each independent claim

All 25 claims are apparatus claims. Independent claims are 1, 6, 9, 11, 16, 17, and 21–25 (claims 2–5, 7–8, 10, 12–15, and 18–20 depend from them). Each independent claim recites the same basic layer stack and differs mainly in (i) the claimed dimensional window, (ii) whether an energy value is included, and (iii) whether the claim is directed to the chip alone, a printhead, or a printer.

• Claim 1 (heater chip): The layer stack as above; heater area (length × width) from about 50 to less than 250 μm²; heater thickness about 500 to 6000 Å. No energy limitation.
• Claim 6 (inkjet printhead): A housing plus a heater chip attached to it having the same stack; area 50 to less than 250 μm²; thickness about 500 to 5000 Å (upper bound narrower than claim 1).
• Claim 9 (inkjet printer): At least one printhead with an ink supply and the heater chip, held in a carriage that reciprocates over a print zone; area about 50 to about 350 μm²; thickness less than 1100 Å (no stated lower bound).
• Claim 11 (heater chip): Stack where the overcoat is specifically both a passivation layer and a cavitation layer; area 50 to about 350 μm²; thickness 500 to 6000 Å; the heater is adapted to emit an ink drop with an energy pulse of about 0.007 to about 0.83 μJ.
• Claim 16 (heater chip with ink via): Adds an ink via in the substrate adapted to receive ink from the printhead, and defines the heater length by the anode-cathode spacing; overcoat is passivation + cavitation; heater arranged adjacent the via; area 50 to about 350 μm²; thickness 500 to 5000 Å; energy pulse about 0.007 to about 0.69 μJ.
• Claim 17 (heater chip): Broad dimensional cap without lower bounds — area less than about 400 μm²; thickness less than about 4000 Å; energy to emit an ink drop less than about 0.64 μJ.
• Claim 21 (heater chip): Area about 50 to about 500 μm²; thickness about 500 to about 1000 Å (thin-heater window, no energy limitation).
• Claim 22 (heater chip): Area about 50 to about 350 μm²; thickness about 500 to less than about 1000 Å.
• Claim 23 (heater chip): Area less than about 400 μm²; thickness less than 1100 Å.
• Claim 24 (heater chip): Area less than 400 μm² (no "about"); thickness about 500 to about 6000 Å.
• Claim 25 (heater chip): Area about 50 to about 500 μm²; thickness about 500 to less than about 1000 Å (overlaps heavily with claim 21; distinguished principally by the open-ended "less than about 1000 Å" upper bound).

Litigation / post-issuance history (from live search results)

• District court: A case was filed in the U.S. District Court for the Western District of Texas, No. 6:19-cv-00549 (per Unified Patents litigation data linked from Google Patents).
• IPR: IPR2020-01659, HP Inc. v. Slingshot Printing LLC, petition filed 2020-09-20, institution decision 2021-03-29, terminated — settled on 2021-03-29 (per Unified Patents/ipverse data).
• Expiration: The patent shows Expired – Lifetime, with adjusted expiration around 2024-06-11; maintenance fees were paid through the 12th year (2020).

CAFC 2026 docket search — result and uncertainty

I searched CAFC 2026 materials for an appeal specific to patent 7410246 and found no CAFC appeal docket for this patent number in 2026. The 2026 Federal Circuit matters involving Slingshot Printing LLC v. Canon (e.g., appeals 2024-2132 and 25-1032/25-1033, and cases concerning patents 7,290,864; 7,484,823; and 7,594,708) concern different Slingshot printhead patents, not 7,410,246. I did not locate any evidence that 7,410,246 was appealed to the Federal Circuit in 2026. If you need absolute certainty on the absence of a CAFC filing, the USPTO Patent Center and the CAFC docket search (PACER/CourtListener) would be the authoritative confirmatory sources — I cannot fully verify a negative result from the searches performed.

Based on my searches, here is what I can confirm regarding known litigation involving U.S. Patent 7,410,246 B2 (the "7410246" / "US7410246" heater-chip patent; do not confuse with the family-member US6890062B2 or similar numbers):

1. District Court Action

Slingshot Printing LLC v. HP Inc.

• Plaintiff: Slingshot Printing LLC
• Defendant: HP Inc.
• Jurisdiction: U.S. District Court for the Western District of Texas, Waco Division (Judge Alan D. Albright)
• Case No.: 6:19-cv-00549-ADA (later transferred to the Austin Division)
• Filing date: September 20, 2019
• Patents asserted: The complaint asserted ten patents, including U.S. Patent No. 7,410,246 (along with 6,213,587; 6,575,563; 6,676,246; 6,786,575; 7,018,012; 7,195,341; 7,290,864; 7,484,823; and 7,559,629).
• Status/outcome: The case was transferred to the Austin Division by order signed February 19, 2020, remaining before Judge Albright (re-docketed in the Austin Division; related records reference docket 1:20-cv-00187-ADA). The parties reached a global settlement of their dispute in March 2021 (see IPR below), which resolved the district court litigation. I could not confirm the exact dismissal/termination docket entry from the available search results, so the precise "stipulation of dismissal" filing date should be verified on PACER if needed.

2. Inter Partes Review (PTAB)

HP Inc. v. Slingshot Printing LLC

• Petitioner: HP Inc.
• Patent Owner: Slingshot Printing LLC
• Forum: Patent Trial and Appeal Board (PTAB)
• Case No.: IPR2020-01659
• Filing date: September 20, 2020 (petition; notice of accord filing date October 26, 2020)
• Challenge: Inter partes review of U.S. Patent No. 7,410,246 (application no. 10/619,975; Tech Center 2800)
• Status/outcome: Terminated – Settled. The parties filed a Joint Motion to Terminate on March 19, 2021, stating they had settled their dispute and executed a settlement/license/release agreement. The Board had not yet issued an institution decision. The PTAB entered its Termination Decision on March 29, 2021. The settlement agreement was filed as business-confidential. A post-termination refund of the post-institution fee was approved in May 2021.

Additional notes

• The Google Patents record for US7410246B2 independently flags the same two matters: the W.D. Tex. case 6:19-cv-00549 and PTAB case IPR2020-01659 (petitioner HP Inc.), confirming these are the principal U.S. proceedings tied to this specific patent.
• I did not find any other district-court cases or PTAB challenges specifically naming U.S. Patent 7,410,246. Related Slingshot v. HP cases and IPRs exist for other patents in the same family/campaign (e.g., IPR2020-01084/01085/01086/01090 challenging other patents), but those do not involve 7,410,246 and should not be conflated with it.

Caveat: My searches were limited to publicly indexed sources. If you need the definitive final disposition of the district court docket (e.g., the exact stipulation-of-dismissal date and whether it was with prejudice), that should be pulled directly from PACER for case 6:19-cv-00549 / 1:20-cv-00187-ADA, or from the Unified Patents litigation portal.

Proceedings overview

Total known proceedings: 1 — all statuses: 0 active, 0 claims invalidated, 0 claims sustained on the merits, 1 settled (terminated pre-institution), 0 institution-denied. The sole AIA trial proceeding against US 7,410,246 — IPR2020-01659 (HP Inc. v. Slingshot Printing LLC) — was terminated by settlement on 2021-03-29 before the Board ever decided institution, so no claim was canceled and no merits finding was ever made. Bottom line for a defendant: every one of the 25 claims remains fully in force and none has been "hardened" or "killed" by an IPR merits decision — the patent is simply untested, and the one petitioner (HP) took a license and walked away.

⚠️ Data-source discrepancy (flagged): The structured "PTAB proceedings on file" block states the USPTO Open Data Portal API returns no AIA trial proceedings for this patent as of its most recent ingest. That is contradicted by live web sources — Google Patents' own record, DocketAlarm, ipverse, and Unified Patents all independently confirm IPR2020-01659 on this exact patent (app. 10/619,975). Treat the ODP block as stale/not-yet-ingested for this patent and IPR2020-01659 as the one on-file proceeding.

IPR2020-01659 — HP Inc. v. Slingshot Printing LLC

• Type: Inter Partes Review
• Filed: 2020-09-20 (petition; Notice of Filing Date Accorded issued 2020-10-26)
• Status: Terminated-Settled (per DocketAlarm/ipverse/Unified Patents) — plain-English gloss: the parties settled the whole dispute and the Board dismissed the case before deciding whether to institute review; no merits decision was ever reached.
• Judge panel: Per DocketAlarm's docket listing — APJs Garth Baer, John Hamann, and Stacy B. Margolies (Tech Center 2800, Art Unit 2853). Because the case ended pre-institution, no panel decision on the merits exists.
• Petition grounds: The petition (titled "Petition for IPR of U.S. Patent No. 7,410,246 (Claims 1, 6–8, 24)") challenged claims 1, 6, 7, 8, and 24 (independents 1 and 24 plus printhead claim 6 and its dependents 7–8). The primary reference was U.S. Patent No. 6,309,052 ("Prasad et al.," "High thermal efficiency ink jet printhead," HP) — asserted both as § 102 anticipation (Ground 1: Prasad allegedly discloses every element of claims 1, 6–8, 24, including a ~900 Å TaAl resistor, ~10 µm × 20 µm (≈200 µm²) heater segments, and an overcoat/passivation stack yielding a heater thickness of ~4,400–5,400 Å) and as § 103 obviousness (Ground 2: Prasad alone, with the "overcoat layer" limitation alternatively obvious over Prasad in view of U.S. Patent No. 6,126,277 ("Feinn"), which teaches cavitation-layer-free SiC-over-resistor chambers). Petitioner's expert was Stephen F. Pond, Ph.D. (Ex. 1002); the May 1985 Hewlett-Packard Journal (Ex. 1007) was also of record. Caveat: the complete ground-by-ground list was never adjudicated, so I cannot verify every alternative ground from the public fragments.
• Institution decision: None entered. No institution decision appears on the docket; the case was terminated on joint motion before the Board acted on the petition. Under § 314(b) the decision would have been due ~3 months after the 2020-10-26 accord date, but no institution decision document was ever filed and the case closed by Termination Decision instead.
• Final Written Decision: None. No FWD was issued, so no claim was canceled and no claim was held patentable on the merits. (35 U.S.C. § 318(a) FWD only follows an instituted review.)
• Settlement / termination: The parties filed a Joint Motion to Terminate on 2021-03-19 (with patent owner's Updated Mandatory Notices the same day), stating the dispute had been resolved. They jointly filed Exhibit 1009 — the confidential "Slingshot–HP Settlement License and Release Agreement" (2021-03-19) and a Joint Request to Treat the Settlement Agreement as Business Confidential Information under 35 U.S.C. § 317(b) and 37 CFR § 42.74. The Board entered its Termination Decision on 2021-03-29. HP's post-institution fee was refunded (Board Refund Approval 2021-05-18, following HP's 2021-05-17 request). Settlement terms are confidential.
• Appeal: None. There is no FWD to appeal, and no party appealed the Termination Decision to the Federal Circuit. (The 2026 CAFC Slingshot matters involve different printhead patents — e.g., 7,290,864; 7,484,823; 7,594,708 — not 7,410,246.)
• Defensive value: Limited but real. HP's IPR was dismissed on settlement, not on the merits — so there is no claim-kill to lean on. What the proceeding does tell you: (1) a sophisticated petitioner (HP) thought claims 1, 6–8, and 24 had enough § 102/§ 103 exposure over Prasad/Feinn to spend money on a petition; (2) the patent owner (Slingshot) resolved the entire district-court/IPR war with HP via a license, meaning HP is now a licensee, not an ongoing challenger; and (3) because the IPR never produced a FWD, no § 315(e) estoppel attached — the Prasad/Feinn grounds remain fully available to any new defendant who was never HP's privy (subject only to the § 315(b) one-year bar running from its own service date).

Strategic summary

Claims CANCELED vs. SUSTAINED vs. UNTESTED. No claim of US 7,410,246 has ever been canceled in an AIA trial — the only IPR (IPR2020-01659) settled pre-institution. Likewise, no claim has ever been "sustained" by a merits decision, because no FWD exists. The honest characterization of all 25 claims (independent claims 1, 6, 9, 11, 16, 17, 21–25 and dependents 2–5, 7–8, 10, 12–15, 18–20) is UNTESTED. Claims 1, 6, 7, 8, and 24 were the ones HP targeted; claims 2–5, 9–23, and 25 were never even challenged. This is a patent that has been asserted in litigation but has never faced a merits determination at the PTAB — the opposite of a "hardened" patent.

Estoppel landscape. Because IPR2020-01659 terminated before institution, neither § 315(e)(1) nor § 315(e)(2) estoppel applies to HP (estoppel attaches only after a FWD under § 318(a)). HP is contractually bound by the confidential settlement/license, but as a legal matter the Prasad (US 6,309,052), Feinn (US 6,126,277), and May 1985 HP Journal grounds remain available to any unrelated defendant — provided it files its own petition within one year of being served with a complaint (35 U.S.C. § 315(b)) and can't be treated as HP's privy. A defendant sued now on this patent has a fresh § 315(b) clock and a clear field of prior art (Prasad's 200 Å-adjacent TaAl resistor/overcoat stack is squarely on point for the claimed 50–350 µm² / 500–6000 Å windows). One caution: the patent is expired (adjusted expiration 2024-06-11), so a would-be petitioner's § 315(b)/standing calculus differs — post-expiration, damages are limited to pre-expiration conduct, and an IPR may still be pursued but the economics shift.

Pattern signals. Only one petitioner (HP Inc., a large operating company) filed on this patent, and it settled — consistent with Slingshot's broader 2019–2021 campaign against HP in W.D. Tex. (6:19-cv-00549, later 1:20-cv-00187-ADA), which was resolved globally. Unified Patents appears in the record only as a data provider (its portal flags the case), not as a petitioner or privy. Slingshot did not face repeat IPRs on this patent (the related IPR2020-01084/-01085/-01086/-01090 cluster challenged different Slingshot patents). No defensive-aggregator petition, no serial challenge, no CAFC appeal — this patent's IPR history is a single, settled, pre-institution blip.

Recommended next steps

1. If you are a defendant facing assertion of 7,410,246 today: Do not tell a court "the claims were invalidated in IPR" — they were not. The accurate framing is: (a) the patent is expired (adjusted expiration 2024-06-11), capping damages to pre-expiration conduct; (b) the only IPR (IPR2020-01659) settled pre-institution, leaving no estoppel against you if you are not HP's privy; and (c) HP's own petition (public at the PTAB's PRPS/PTACTS portal, case IPR2020-01659, Exs. 1002–1008) is a ready-made roadmap of the Prasad (US 6,309,052) anticipation/obviousness case against claims 1, 6–8, and 24, and the Feinn (US 6,126,277) teaching that a cavitation layer is unnecessary — art you can press in district court invalidity contentions or a fresh petition within your own § 315(b) window.
2. If you want the primary-source documents: The Termination Decision is DocketAlarm doc. No. 9 (2021-03-29) at docketalarm.com/cases/PTAB/IPR2020-01659/; the petition, Pond declaration (Ex. 1002), Prasad (Ex. 1004), and Feinn (Ex. 1005) are visible via the USPTO PTACTS public-information links and the PTAB E2E/PRPS docket for IPR2020-01659. The settlement agreement itself (Ex. 1009) is confidential — do not expect access.
3. If you are weighing a new IPR: No FWD exists, so § 315(e) is no bar, but check (i) your § 315(b) one-year clock from service, (ii) whether you stand in privity with HP (the settlement/license could create a contractual relationship relevant to that inquiry — investigate), and (iii) whether the Board would exercise discretion given the parallel expired-patent/limited-damages posture. Because the patent expired 2024-06-11, most defendants' practical play will be district-court invalidity using the Prasad/Feinn art rather than a new IPR.
4. If you need absolute certainty on "no other proceedings": The negative in the ODP block should be treated as stale. Confirm against the PTAB's live E2E/PRPS search for patent number 7,410,246 and the USPTO Patent Center for app. 10/619,975. My searches found no second IPR, PGR, or CBM naming this patent — only IPR2020-01659 — but a live PTAB docket check is the authoritative confirmation.

Inventors

Pattern note: All three inventors executed their assignment to Lexmark on the same date (effective 2002-05-09; recorded 2003-07-15 at reel 014287/frame 0489), which is the normal employment-assignment pattern for a corporate filing — not a red flag. Bell and Cornell continued inventing for Lexmark years later (e.g., Cornell's 2004 US 7,316,475 application and Bell's 2008 US 2009/0267996 application), so there is no "inventors depart within 12 months before a portfolio fire-sale" pattern here.

Original assignee

Lexmark International, Inc. — the entity named on the issued patent (recorded as original assignee on 2003-07-15, reel 014287/0489; patent issued 2008-08-12).

• Shipped products embodying the claims? Yes. Lexmark was an operating printer company (IBM spinoff) whose thermal inkjet printheads/cartridges embodied this heater-chip technology. This is not a paper patent at origin.
• Line of business: Printers, inkjet cartridges, and imaging supplies.
• Current status: Operating. Lexmark exited the inkjet business in 2013, selling the inkjet technology/assets (including this patent) to Funai for ~$100M; Lexmark itself was later taken private by Apex/PAG (2016). It is no longer the owner of this patent.

Assignment timeline

Chronology is reconstructed from the USPTO-recorded legal events shown on the Google Patents record (which reproduces the USPTO Assignment Division reel/frame data) and confirmed by a USPTO 37 CFR 3.73(b) statement on file (June 7, 2013) that recites the chain of title. Caveat: the reel/frame data I can verify does not include the "correspondent of record" attorney for each recording; that field is only visible in the scanned cover sheets at the USPTO Assignment Center, which I could not fully retrieve. Correspondent recurrence is therefore marked "unclear" below rather than guessed.

• 2002-05-09 (executed) / recorded 2003-07-15 — Reel 014287/Frame 0489

  • Conveyance: Assignment of Assignors' Interest (inventor → employer)
  • Assignor: Byron Vencent Bell; Robert Wilson Cornell; Yimin Guan
  • Assignee: Lexmark International, Inc.
  • Correspondent: not visible in available data (Lexmark in-house IP Law Dept. handled prosecution; recording correspondent unverified)
  • Context: Standard pre-filing employment assignment; the continuation application (10/619,975) was filed 2003-07-15 and the assignment was recorded the same day.

• 2013-04-01 (effective) / recorded 2013-05-14 — Reel 030416/Frame 0001

  • Conveyance: Assignment of Assignors' Interest (portfolio sale)
  • Assignor: Lexmark International, Inc. and Lexmark International Technology, S.A.
  • Assignee: Funai Electric Co., Ltd. (Japan)
  • Correspondent: not visible in available data
  • Context: Lexmark's ~$100M exit from inkjet — over 1,500 US/foreign patent assets moved to Funai, which acquired Lexmark's inkjet technology, cartridge manufacturing, and related assets. A 37 CFR 3.73(b) statement (signed 2013-06-07 by Funai's Senior General Manager of IP) confirmed this chain of title to the USPTO.

• 2019-03-29 (executed and recorded) — Reel 048745/Frame 0551

  • Conveyance: Assignment of Assignors' Interest (transfer-to-asserter)
  • Assignor: Funai Electric Co., Ltd.
  • Assignee: Slingshot Printing LLC
  • Correspondent: not visible in available data
  • Context: Funai transferred more than 100 US inkjet-patent assets to recently formed Slingshot Printing LLC, which had no product business and began asserting the patents within months (RPX: "assignment records suggesting that Funai might hold an economic interest in Slingshot's litigation").

No other assignments, mergers, security agreements, licenses, or name changes are recorded for this patent. The chain has exactly three links: inventors → Lexmark → Funai → Slingshot.

Timeline diagram

timeline
    title Ownership of US 7410246
    2002 : Inventors assign to Lexmark
    2003 : Continuation filed
         : Assignment recorded
    2008 : Patent issued to Lexmark
    2013 : Lexmark sells inkjet assets to Funai
    2019 : Funai assigns to Slingshot Printing LLC
         : Slingshot sues HP in West Texas
    2020 : HP files IPR2020-01659
    2021 : IPR terminated after settlement
    2024 : Patent expires

NPE / troll-pattern signals

1. Shell-entity transfer — present. Recorded 2019-03-29, reel 048745/0551: Funai (an operating manufacturer) transferred >100 US patents including 7,410,246 to Slingshot Printing LLC, a newly formed entity with no products in commerce. RPX classified Slingshot as an NPE and reported it "began litigating former Lexmark patents" within weeks of receiving them. The single-purpose LLC formed to hold and assert a defined patent pool is the functional equivalent of the "IP Holdings" shell tell even though the name omits "IP."

2. Known asserter in the chain — present. Slingshot Printing LLC is a high-frequency plaintiff (Slingshot v. HP Inc., W.D. Tex. 6:19-cv-00549, filed 2019-09-20, asserting ten patents including 7,410,246; later Slingshot v. Canon matters) and is tracked as an NPE by RPX and Unified Patents. HP challenged the patent in IPR2020-01659 (petition filed 2020-09-20), which terminated on settlement 2021-03-29.

3. Repeat correspondent across the chain — unclear. The USPTO reel/frame summaries I can access do not disclose the recording correspondents. (For reference, PTAB counsel for Slingshot in IPR2020-01659 was Michael Siem; HP was represented by Barry Shelton — but litigation counsel is not the same as the assignment correspondent of record.) This signal should be checked against the scanned cover sheets at the USPTO Assignment Center; I could not verify it and will not fabricate names.

4. Cascading transfers — not present in the classic sense. The three recorded assignments span 2002→2013→2019 (6+ years apart), not chained LLC transfers within 24 months.

5. Pre-litigation transfer — present. The Funai → Slingshot assignment was recorded 2019-03-29 (reel 048745/0551) and the first infringement suit naming this patent, Slingshot v. HP (6:19-cv-00549, W.D. Tex.), was filed 2019-09-20 — under six months later, and RPX records earlier Slingshot filings against HP in June 2019 on sibling patents. The transfer was arranged immediately before assertion, consistent with standing/venue preparation.

6. Bankruptcy fire-sale — not present. Lexmark's 2013 divestiture to Funai was a negotiated business exit (inkjet discontinued, assets sold for ~$100M), not a Chapter 7/11 patent sale. No bankruptcy event is in this chain.

7. Privateering — present. Funai, an operating company that continued manufacturing inkjet hardware (including Kodak-brand printers from 2015), transferred the patents to Slingshot, which then sued competitor HP. RPX specifically reported that "assignment records suggest that Funai might hold an economic interest in Slingshot's litigation" — the hallmark operating-company-to-NPE privateering structure.

8. Defensive aggregator (anti-NPE) — not present. The chain terminates at Slingshot Printing LLC, an asserting entity. The patent is not held by RPX, AST, LOT, Unified Patents, or OIN (and is now expired, as of ~2024-06-11, which moots further assertion).

Verdict

NPE — high confidence.

Three strong signals converge: (1) the 2019-03-29 transfer at reel 048745/0551 moved the patent from operating company Funai to newly formed, product-less Slingshot Printing LLC — an entity RPX and Unified Patents track as an NPE that immediately sued HP (W.D. Tex. 6:19-cv-00549, filed 2019-09-20) asserting this patent; (2) that suit came under six months after the transfer (pre-litigation transfer); and (3) RPX reported assignment records suggesting Funai retained an economic interest in Slingshot's litigation — the classic privateering structure. The one unverified element is correspondent-of-record recurrence, which requires the Assignment Center cover sheets; the remaining evidence is sufficient on its own. Verify the underlying recordings at the USPTO Assignment Center: https://assignmentcenter.uspto.gov/ (search Patent No. 7410246; reels 014287/0489, 030416/0001, 048745/0551).

USPTO search for the exact patent number 7410246 — confirmation

I searched specifically for 7410246 (not for similar numbers) and confirmed the target document is US 7,410,246 B2, "Heater chip configuration for an inkjet printhead and printer" (Bell, Cornell, Guan; Lexmark; app. 10/619,975; filed 2003-07-15; issued 2008-08-12). The USPTO/Google Patents/Justia records for this exact number all agree on the references list below.

Numbers excluded deliberately (do not confuse): several near-similar documents surfaced and were set aside because they are not citations of 7410246 and are not the target patent: US 6,139,130 (Canon — note: distinct from the cited US 6,139,131, an easy typo trap), US 6,890,062 (the sibling family member of 7410246), US 8,400,257 (a later STMicro patent that merely cites 7410246), and the various 6,575,563 / 7,290,864 / 7,484,823 Slingshot-suit patents asserted alongside 7410246. None of those is a citation of 7410246.

The prior-art citations of US 7,410,246

The face of the patent lists six "Patent Citations" (five U.S. + one Japanese). The Google Patents record additionally lists three "Family Cites Families" references (cited on the family, e.g., the sibling US 6,890,062). All nine are treated below because the IPR record shows the family-level Prasad reference matters.

A. The six references printed on the face of 7410246

1. US 4,338,611 A — "Liquid jet recording head" (Eida et al., Canon)

• Filing date: 1980-09-12 (app. 06/186,581) · Publication date: 1982-07-06
• Brief description: One of Canon's foundational bubble-jet head patents. Discloses a substrate (base plate 111) carrying an electro-thermal transducer (110) built as: a lower heat-accumulating/flow-control layer (115, i.e., a thermal-barrier analog), a heat-generating resistive layer (116), and an upper protective layer (117), with common and selection electrodes (118, 119) over the resistor. Claims are directed to dimensional relationships (L, l, a, b) of the liquid flow path, with energy-acting-zone length l = 10–800 µm.
• § 102 potential: Low for any claim. It predates the claimed thin-film heater-chip paradigm and discloses none of the claimed numerical windows (heater area 50–350/500 µm², heater thickness 500–6000 Å) or the energy values. It does not disclose a conductor layer whose spacing alone defines a heater length in the claimed sense with the claimed overcoat-thickness/resistor-thickness summation. Examiner use is best characterized as background art (early B41J2/1412-type resistive-element art). It does not plausibly anticipate any claim standing alone.

2. US 4,567,493 A — "Liquid jet recording head" (Ikeda et al., Canon)

• Filing date: 1984-04-11 (priority 1983-04-20 JP) · Publication date: 1986-01-28
• Brief description: Canon bubble-jet head with a multi-layer upper protection scheme over an HfB₂ heat-generating resistive layer: a first upper protection layer of inorganic insulator (SiO₂-type) = passivation, a second organic layer outside the heat-generating portion, and a third upper protection layer of Ta over the heat-generating portion = cavitation layer. Also discloses the SiO₂ underlayer on the silicon/glass/ceramic support, Al electrodes, and a heat-generating portion defined between the electrodes. This is the classic "passivation + cavitation overcoat" teaching.
• § 102 potential: Moderate for structural sub-elements only; low for any full claim. It squarely reads on the overcoat = passivation layer + cavitation layer limitation found in claims 2, 11, 16, and 18 (and the dielectric-passivation limitations of dependent claims 3, 12, 19, and the Ta-cavitation limitation of claim 14). But it nowhere discloses the claimed heater-area/thickness numerical windows or the energy-pulse ranges. Anticipation of claims 11/16 (which pair the passivation+cavitation overcoat with 50–350 µm² / 500–6000 Å / 500–5000 Å windows and 0.007–0.83/0.69 µJ energy) fails on the numbers. It is far stronger as a § 103 secondary reference for the overcoat element than as a § 102 anticipatory reference.

3. US 4,635,073 A — "Replaceable thermal ink jet component and thermosonic beam bonding process for fabricating same" (Hanson, Hewlett-Packard)

• Filing date: 1985-11-22 (app. 06/801,034) · Publication date: 1987-01-06
• Brief description: HP's seminal thin-film thermal printhead substrate. Discloses, in the exact order later claimed by 7410246: a silicon substrate (40); a silicon dioxide layer (42) for passivation/thermal isolation (thermal-barrier analog); a tantalum-aluminum (TaAl) resistive layer (44) photolithographically defined into heater resistors; aluminum conductive traces over the resistor layer whose terminations bound the resistor heating regions; and a silicon-carbide (SiC) barrier/overcoat layer (46) over the TaAl resistors. It also discloses the ink-feed slot (12) in the substrate (via analog), a TAB circuit, and a replaceable pen component. This is the earliest direct structural ancestor of the 7410246 layer stack.
• § 102 potential: Highest of the older references for the structural elements. Element-by-element, it reads on the preamble + stack of claims 1, 6, 9, 11, 16, 17, and 21–25: substrate → SiO₂ thermal barrier → resistor layer (width defines heater width) → Al conductor (length defined by conductor edges) → overcoat over the resistor. What is missing from the record is an explicit disclosure of the claimed numeric windows (heater area 50–350 µm²; heater thickness 500–6000 Å with the overcoat+resistor sum; energies in µJ). Whether its actual resistor/overcoat dimensions fall inside the windows (HP's TaAl films in this era were on the order of ~1000 Å, and heater sizes were tens of µm) would require reading the full text; the excerpts retrieved do not state the numbers. If the dimensions are shown to land in the claimed windows, this reference would be a genuine § 102 candidate for claims 1, 6, 17, and 21–25; otherwise it is the closest structural § 103 anchor.

4. JP 4-255357 A — "Ink flying recording device" (Ricoh)

• Filing date: 1991-02-07 (laid-open publication 1992-09-10)
• Brief description: Japanese kokai (unexamined laid-open application) for an ink-flying recording device. I could not retrieve the full text or an abstract from the searches performed, so I cannot responsibly describe its teachings in detail or map it to claims.
• § 102 potential: Unverifiable from the search record. It appears in the citation list as field art (B41J2/14-class thermal/ejection devices). Treat it as background until the Japanese document is pulled (J-PlatPat/Espacenet). I will not fabricate a claim mapping.

5. US 5,270,730 A — "Jet recording method and apparatus for discharging normally solid recording material by causing generated bubble to communicate with ambience" (Yaegashi et al., Canon)

• Filing date: priority 1990-09-29 · Publication date: 1993-12-14
• Brief description: Phase-change / hot-melt ("normally solid") ink jet recording. A heater is disposed along a nozzle path to melt the ink and generate a bubble that ejects a droplet, with the bubble communicating with the ambience. The inventive focus is the ink formulation (Tm 40–150 °C / Tb 260–340 °C; Tm − Tf ≤ 30 °C) and the bubble-ambience communication method, not the thin-film heater-chip layer stack.
• § 102 potential: Low for every claim. It discloses none of the claimed layer architecture (thermal barrier/resistor/conductor/overcoat with the width/length/thickness definitions) and none of the claimed dimensional or energy windows. Examiner use was evidently for bubble-formation/ambient-communication background. It does not plausibly anticipate any of claims 1–25.

6. US 6,139,131 A — "High drop generator density printhead" (Prasad et al., Hewlett-Packard)

• Filing date: 1999-08-30 · Publication date: 2000-10-31
• Brief description: HP's high-density thermal inkjet printhead — the direct commercial/technical predecessor line to the Lexmark 7410246 chip. It addresses shrinking heater footprint for high drop-generator density, using thin-film TaAl resistor heaters and passivation/overcoat stacks on a silicon substrate with ink-feed slots. This is the closest in time and subject matter of the six face citations, and shares inventors' corporate lineage with the art HP later pressed in IPR2020-01659.
• § 102 potential: Highest overall. This is the reference most plausibly disclosing the claimed combination: a small-area high-density heater chip whose TaAl resistor thickness and overcoat stack plausibly land within the claimed 500–6000 Å heater-thickness window, and whose heater areas plausibly land within the claimed 50–350/500 µm² (and possibly the <250 µm²) windows of claims 1, 6, 21–25. It therefore is the strongest § 102 candidate against claims 1, 6, 9, 17, 21–25 (structure + geometry), assuming the full text confirms the numerical ranges — which I could not fully verify from the excerpts retrieved. Note carefully: do not confuse US 6,139,131 with US 6,139,130 (Canon, same publication date, different patent, different assignee) — 7410246 cites the HP patent 6,139,131.

B. The three "Family Cites Families" references (cited on the family, relevant context)

7. US 6,309,052 B1 — "High thermal efficiency ink jet printhead" (Prasad et al., Hewlett-Packard)

• Filing date: 1999-04-30 · Publication date: 2001-10-30
• Brief description & relevance: This is the primary reference HP used in IPR2020-01659 against claims 1, 6, 7, 8, and 24 of 7410246 (per the petition record summarized earlier: HP alleged Prasad discloses a ~900 Å TaAl resistor, ~10 µm × 20 µm (~200 µm²) heater segments, and an overcoat/passivation stack yielding a heater thickness of ~4,400–5,400 Å — i.e., inside the claimed 50–350 µm² / 500–6000 Å windows). The IPR settled pre-institution, so no merits finding ever confirmed or rejected that anticipation theory, and no § 315(e) estoppel attached.
• § 102 potential: Very high — the art HP itself bet on. If Prasad's dimensions are as HP characterized them, it is a strong § 102(a)/(e) anticipation candidate for claims 1, 6, 7, 8, and 24 (and by extension structurally similar claims 9, 17, 21–23, 25, subject to their differing windows and the energy limitations of claims 11/16/17). This remains the single most dangerous prior-art reference identified anywhere in the record.

8. DE 30 11 919 A1 — "Method for producing a recording head" (Canon)

• Filing date: priority 1979-03-27 · Publication date: 1980-10-09
• Brief description: German family member of early Canon bubble-jet recording-head manufacturing art (relates to the same disclosure family as US 4,338,611).
• § 102 potential: Low. Background manufacturing/head art; none of the claimed numeric windows. Useful only as cumulative early art.

9. US 6,676,246 B1 — "Heater construction for minimum pulse time" (Lexmark International)

• Filing date: 2002-11-20 · Publication date: 2004-01-13
• Brief description: Lexmark's own later heater-construction work (minimum pulse time).
• § 102 potential: None for 7410246. Filed 2002-11-20, which is after 7410246's priority date of 2002-05-14 — it cannot be § 102 prior art against 7410246. It appears in the family-citation list because it was cited in related/family prosecutions. Do not rely on it for invalidity of this patent.

Claim-mapping summary (which claims each reference potentially anticipates under § 102)

Bottom line for the § 102 analysis: The two HP Prasad patents — US 6,139,131 (face citation) and US 6,309,052 (family citation and the settled-IPR primary reference) — are the only references with a realistic chance of fully anticipating the range-limited independent claims, and only if their disclosed heater dimensions are confirmed to fall inside the claimed 50–350/500 µm² area and 500–6000 Å thickness windows (and, for the energy-limited claims 11/16/17, that the energy figures are inherent or disclosed). US 4,635,073 is the closest early structural art. US 4,567,493 supplies the passivation+cavitation overcoat element. The Canon-era and Ricoh references are background/field art. One important doctrine caveat: a prior-art range that merely overlaps a claimed range generally does not anticipate unless the reference specifically discloses the claimed point or range — so each Prasad analysis will turn on whether specific dimensions (e.g., HP's ~200 µm² / ~900 Å resistor values) are actually stated or inherent in the reference text.

Verification caveats (stated plainly): (1) I could not retrieve the full text of JP 4-255357 A or the complete specification of US 6,139,131 / US 6,309,052 from the searches performed, so the numeric disclosures for those references should be confirmed against the primary sources (USPTO Patent Center / PTAB E2E for IPR2020-01659, Exhibits 1002–1008). (2) The "which claims" mappings above are structural-read analyses, not findings that anticipation was proven — the IPR settled before any institution decision, so no court or Board has ever adjudicated any of these references against any claim of 7410246.

I'll analyze obviousness of US 7,410,246 under 35 U.S.C. § 103. Let me first ground my analysis in the cited prior art and any relevant details about the references used in the IPR petition.

Let me gather more detail on the Prasad reference's heater structure (used in the IPR petition) and the other cited references.

Let me look at the Lexmark family-cited reference and other cited art relevant to combination analysis.

§ 103 Obviousness Analysis — US 7,410,246 B2 ("Heater chip configuration for an inkjet printhead and printer")

1. Scope, ground rules, and evidentiary notes

• Priority date: 2002-05-14 (parent 10/146,578). Everything in this analysis measures prior-art status against that date under pre-AIA § 102.
• The claims are all apparatus claims to a thin-film heater chip stack (substrate → thermal barrier → resistor layer whose width = heater width → conductor layer whose anode/cathode spacing = heater length → overcoat; combined overcoat + resistor thickness = "heater thickness" TH). What separates the 25 claims is almost entirely the numerical window on heater area (LH × WH) and heater thickness (TH), plus, in a subset, a per-drop energy bound and/or the presence of a passivation + cavitation overcoat, an ink via, or printhead/printer context.
• Critical timing flag: one reference appearing in the patent's own family-cite list — US 6,676,246 B1 ("Heater construction for minimum pulse time," Lexmark) — was filed 2002-11-20, i.e., after the 2002-05-14 priority date, and claims no earlier benefit. It is therefore not § 102/§ 103 prior art against this patent. It is useful only as co-owned, later-filed evidence of the same design trajectory (thin TaAl resistors, ~7200 Å protective-layer cap, 2.9–4.0 GJ/m³ energy density, 0.73 µs pulse), not as a reference. I flag this because its presence in the citation list could mislead.
• I rely on: (a) the six U.S./JP references cited on the face of the patent; (b) the family-cited art; and (c) the public IPR2020-01659 record (HP's petition, the Pond declaration, and PTACTS document excerpts surfaced in search), which supplies the most precise teaching-level detail for US 6,309,052 (Prasad) and US 6,126,277 (Feinn). Where a numeric teaching comes from the IPR record rather than the printed reference, I say so.

2. Person of ordinary skill in the art (POSITA)

A POSITA would be a design engineer or thin-film process engineer with a B.S./M.S. in electrical engineering, materials science, or physics and 2–5 years in thermal inkjet head design — conversant in: thin-film resistor materials (TaAl, TaN, HfB₂) and sheet resistance; passivation/cavitation layer dielectrics (SiC, Si₃N₄, Ta) and their thickness trade-offs; drop-generator scaling; the relationship between turn-on energy (TOE), resistor resistance, and heater volume; and ink-chamber fluidics/kogation. This profile matches the authorship of the HP art (Prasad; 6,139,131) and the Lexmark/HP inventor communities.

3. Prior-art inventory (all but US 6,676,246 are § 102(a)/(e) prior art to the 2002-05-14 date)

Takeaway from the inventory: the closest art is HP's own trio — Prasad (6,309,052), 6,139,131, and Feinn (6,126,277) — all directed to the same problem the '246 patent solves (low per-drop energy + high density + thin protective stacks for stable jetting), all pre-2002, and two of them commonly assigned. This is precisely the configuration HP's IPR2020-01659 petition exploited, and it is the right lens for the § 103 analysis.

4. Claim groups and the limitations that actually matter

• Group A — structural area/thickness claims (no energy bound): claims 1 (area 50 to <250 µm²; TH 500–6000 Å), 6 (printhead; same area; TH 500–5000 Å), 7–8 (dependents: ink via; TAB), 24 (area <400 µm²; TH 500–6000 Å).
• Group B — energy-bound claims: claims 11 (area 50–350 µm²; TH 500–6000 Å; overcoat = passivation + cavitation; energy pulse 0.007–0.83 µJ), 16 (+ ink via; TH 500–5000 Å; energy 0.007–0.69 µJ), 17 (area <400 µm²; TH <4000 Å; energy <0.64 µJ), and dependent claim 4 (0.007–0.06 µJ).
• Group C — thin-stack claims: claims 21/25 (area 50–500 µm²; TH 500–1000 Å), 22 (area 50–350 µm²; TH 500 to <1000 Å), 9 (printer; area 50–350 µm²; TH <1100 Å), 23 (area <400 µm²; TH <1100 Å).

Because the claimed layer stack (substrate → thermal barrier → resistor → conductor → overcoat) is the generic thermal-inkjet heater chip architecture — disclosed in essentially every reference above (Prasad Figs. 6A/6B and col. 7; 6,139,131's passivation-over-resistor stack; Canon 4,567,493) — the patentability battleground is the numerical windows, not the presence of the layers. That makes this a classic "range selection / result-effective variable" § 103 case, where the applicant's own specification (Figs. 10–12; the 1.5×10¹⁵ W/m³ and "knee-bend" disclosures) concedes energy is a continuous function of heater area × thickness.

5. Combination 1 — Prasad (6,309,052) alone, and Prasad + Feinn (6,126,277)

Mapping (Prasad alone, Group A claims):

• Substrate + thermal barrier: Prasad's silicon substrate with insulating oxide/PSG underlayer (~17,000 Å composite per IPR expert reading of Prasad col. 7).
• Resistor layer / width = heater width: Prasad's patterned ~900 Å TaAl (27.1–31.5 Ω/sq), width defining the current path between conductors.
• Conductor layer / length: Prasad's conductors over the TaAl define the exposed resistor span (heater length); ~10 µm × 20 µm ≈ 200 µm², inside claim 1's "50 to less than 250 µm²" and claim 24's "<400 µm²."
• Overcoat: Prasad's passivation stack (claims 26: < 5000 Å) over the resistor. Resistor 900 Å + passivation ≤ ~5000 Å ⇒ TH ≈ up to ~5900 Å, within claim 1's 500–6000 Å window (and within claim 24's 500–6000 Å); where the realized passivation is ~3500–4500 Å, TH ≈ 4400–5400 Å, also inside claim 6's 500–5000 Å upper bound (the IPR petition took exactly this position on claims 1, 6, 7, 8, 24).

Why Prasad alone is sufficient for Group A (or, at minimum, renders them obvious): HP's petition asserted anticipation by Prasad of claims 1, 6–8, 24. Even if a court found a given Prasad embodiment to sit at the top of (or marginally above) a claimed window rather than cleanly inside it, the § 103 fallback is strong: Prasad expressly teaches the two design dials the '246 claims are just ranges on — thin TaAl (~900 Å) for high resistance, passivation "less than about 5000 Å" (claim 26), and energy minimization below 0.8–1.0 µJ/drop. Tuning resistor width/length between 50 and 350 µm² and overcoat thickness within the disclosed sub-5000 Å bound to land inside any claimed window is a routine, result-effective optimization with a reasonable expectation of success, not an inventive step. KSR v. Teleflex (2007) forecloses treating such disclosed-range optimization as non-obvious merely because the patentee drew a narrower box inside the prior art's disclosed box.

Mapping (Prasad + Feinn, claims 1–8, 24 — and the overcoat/cavitation variants):

• Feinn supplies what Prasad's Fig. 6B embodiment may not cleanly teach for every claim: a cavitation-free overcoat (only SiC + Si₃N₄ passivation, no Ta cavitation layer). Feinn's composite passivation of 3300–4200 Å + Prasad's 900 Å TaAl resistor ⇒ TH ≈ 4200–5100 Å, squarely inside the 500–6000 Å windows of claims 1 and 24; Feinn's 17 × 17 µm resistor (~250–328 µm²) satisfies claim 24's "<400 µm²" (nominal 289 µm²) and, with modest resizing, claim 1's "<250 µm²" window.
• The IPR expert declaration reached exactly this conclusion: "Feinn in view of Prasad discloses every limitation of claim 24 of the '246 patent."
• Motivation to combine Prasad and Feinn (strong): (i) same art, same problem (low TOE, high density); (ii) common assignee (HP), contemporaneous filings — the expert's opinion that a POSITA would read Feinn's unspecified resistor thickness as ~900 Å via Prasad's resistivity/thickness teaching rests on this; (iii) Feinn's raison d'être — removing the cavitation layer to cut turn-on energy — is the same energy-reduction objective Prasad pursues by thinning the passivation and raising resistance; (iv) the references are physically compatible (both HP thin-film stacks on silicon with TaAl resistors and SiC/Si₃N₄ passivation). A POSITA combining them has a reasonable expectation of a working, lower-energy, cavitation-tolerant head — indeed HP shipped products on this architecture.

Claims 2–5, 12–15, 18–20 (dependents): add nothing inventive beyond the base claims — overcoat = passivation + cavitation (Prasad/6,139,131 both show Ta cavitation layers; 6,139,131 claims Ta cavitation 2500–3500 Å), dielectric passivation materials (SiC/Si₃N₄ — 6,139,131 claims them explicitly), resistor compositions (TaAl, TaN, Ta₂N, HfB₂, WSi(O) — Prasad teaches TaAl; 6,139,131 teaches 27.1–31.5 Ω/sq TaAl), anode/cathode-defined length (generic to all references), ink via in substrate (Prasad/6,139,131's fluid-feed architectures; claim 8's TAB circuit is taught by HP's own US 4,635,073). Once the base claim falls, these fall with it.

Net: Group A claims (1, 6–8, 24) are the most vulnerable — Prasad alone (anticipation or obviousness) and Prasad + Feinn both map element-for-element onto the layer stack and dimensional windows, with express motivation. This is consistent with HP having spent the money to challenge exactly these five claims and no others.

6. Combination 2 — Prasad / 6,139,131 / Feinn for the energy-bound claims (11, 16, 17; dependent 4)

These claims add per-drop energy ceilings (≤0.83 / ≤0.69 / <0.64 µJ) and, for 11 and 16, a passivation + cavitation overcoat. The analysis here is more layered:

Reference energies: 6,139,131 teaches 1.0–1.4 µJ/drop (above the ceilings); Prasad claims "<1.0 µJ" and "<0.8 µJ" and its specification's whole thrust is "minimum energy needed to eject an ink drop" via ≥70 Ω high-resistance resistors; Feinn reduces TOE further by eliminating the cavitation layer.

Why a POSITA would have had a reasonable expectation of reaching ≤0.83 / ≤0.69 / <0.64 µJ:

• All three HP references treat per-drop TOE as a design variable controlled by resistor geometry and protective-stack thickness — 6,139,131 states flatly that protective layers "tend to increase the inherent turn-on energy," and Prasad claims the energy ceilings directly. The '246 patent's own specification concedes energy is a function of area × thickness (Figs. 10–12; eqn. 1). Choosing a 50–350 µm² heater and a 500–6000 Å (or <4000 Å) stack from within Prasad's/6,139,131's disclosed envelopes yields per-drop energies at or below the claimed ceilings as a matter of routine scaling — TOE scales roughly with heater area and with protective-layer thermal mass, both of which the art teaches to shrink.
• Combining Prasad's high-resistance, low-energy (<0.8 µJ) teaching with Feinn's cavitation-layer elimination ("significantly reduces the turn on energy") gives a concrete, two-step roadmap to sub-0.7 µJ operation.
• But the honest caveat: the printed HP art is explicit that its production energy is 1.0–1.4 µJ (6,139,131) or "<0.8–1.0 µJ" (Prasad claims) — above the 0.64–0.83 µJ ceilings and far above dependent claim 4's 0.007–0.06 µJ. HP chose not to challenge claims 11, 16, or 17 in IPR2020-01659, which is a meaningful real-world signal that these energy ceilings are the claims' strongest feature. A challenger would need to lean on (a) inherency/continuity arguments (the very small-area, thin-stack embodiments the '246 claims necessarily fire below 0.7 µJ — energy being a consequence of the claimed geometry, per the specification itself), or (b) a declaration quantifying that Prasad's own ~200 µm²/4400–5400 Å embodiment fires at ≤0.64 µJ. Ground (a) is the stronger theory and finds support in the '246's own FIGS. 10–12, but it is untested — no FWD exists (IPR settled pre-institution), so no fact-finder has endorsed or rejected it.
• Dependent claim 4 (0.007–0.06 µJ) sits far below everything the art quantifies; it is the least vulnerable to this combination on the present record.

Net: Claims 11, 16, 17 are vulnerable in theory (result-effective-variable scaling from Prasad/Feinn/6,139,131) but are the claims where the prior art's own numbers leave the largest gap, which is why they were not petitioned. A § 103 case against them needs expert quantification, not just element mapping.

7. Combination 3 — thin-stack claims (21, 22, 25; 9, 23): TH ≤ ~1000–1100 Å

These claims cap total heater thickness (resistor + overcoat) at 500–1000 Å (21, 22, 25) or <1100 Å (9, 23) — i.e., a ~500–1000 Å resistor with at most a few hundred Å of overcoat. This is the hardest window on the cited art:

• Prasad teaches a 900 Å resistor but plus a passivation of up to ~5000 Å (TH ≈ 4400–5900 Å).
• Feinn teaches removing the cavitation layer but keeps SiC + Si₃N₄ of 3300–4200 Å (TH ≈ 4200–5100 Å with Prasad's 900 Å resistor).
• 6,139,131 teaches passivation of 3350–4350 Å (+ optional 2500–3500 Å Ta) — thick, not thin.
• No cited reference discloses (or claims) a total heater stack under ~1100 Å. The art's uniform direction is that ink is chemically corrosive and bubble collapse is mechanically destructive — 6,139,131's background teaches that passivation and cavitation layers are needed precisely to protect the resistor, which is why every production embodiment keeps the protective stack in the thousands of Å.

Motivation arguments available (and their weaknesses):

• 6,139,131's teaching that protective layers increase TOE, plus Feinn's demonstrated step of removing one protective layer entirely (the cavitation layer), could be extended by a POSITA to thinning the remaining passivation — each step reduces TOE and thermal mass. Under KSR's "obvious to try" / predictable-variation logic, a challenger would argue the sub-1100 Å stacks are just the endpoint of the art's own energy-reduction vector.
• Counterweight (honest): the record contains no reference teaching a passivation thin enough to hold TH ≤ ~1000 Å, and the cited art affirmatively warns that too little protection shortens heater life (the '246 itself admits a cavitation-free heater "wear[s] out faster because of corrosive effects from ink"). A court could find that a POSITA had no reasonable expectation of success — or affirmative reason not to go there — for the ultra-thin Group C window, particularly where no stated problem (density, energy, frequency) in the art demanded sacrificing the protective stack to <1100 Å total. These claims (21, 22, 25, 9, 23) are the most likely to survive a § 103 challenge built on the cited art. HP's petition conspicuously left them alone.

8. Why the combinations are legally sound — motivation synthesis

For the combinations that work (Groups A and B), the motivation-to-combine showing is unusually strong:

1. Same field, same problem. Every primary reference is a thermal inkjet printhead/heater-chip patent addressing drop ejection via thin-film resistive heaters. There is no "analogous-art" hurdle.
2. Common assignee / cross-pollination. Prasad (6,309,052), 6,139,131, and Feinn (6,126,277) are all HP patents filed 1999–2001; the IPR expert credibly used Prasad to supply the resistor thickness Feinn leaves implicit because they are contemporaneous HP disclosures. Combining them is closer to reading one HP design file than to a mosaic of strangers.
3. Express, convergent design incentives. Every reference states the same objective the '246 patent claims to achieve: high-density drop generators operated at minimum energy per drop. 6,139,131: energy must be reduced "for higher frequencies and greater drop generator densities to be realized"; Prasad: "lowering the energy dissipated from each firing resistor and the energy required by each firing resistor to eject an ink drop"; Feinn: eliminate the cavitation layer to "significantly reduc[e] the turn on energy." A POSITA combining them to arrive at a 50–350 µm², ~500–6000 Å heater firing below 1 µJ is following the art's explicit roadmap, not exercising invention.
4. The claimed ranges are result-effective variables disclosed by the art. The '246 specification itself defines energy as a monotone function of heater area and thickness (eqn. 1; Figs. 10–12; power/volume threshold of 1.5×10¹⁵ W/m³). Where prior art discloses the controlling variables and the direction of optimization (thinner, smaller, higher-resistance), a patentee cannot capture every intermediate range as its own — the claimed 50–350 µm² / 500–6000 Å / ≤0.83 µJ boxes sit inside envelopes Prasad and 6,139,131 already opened.
5. Reasonable expectation of success. HP's own shipped high-density, sub-µJ, thin-passivation printheads (the subject of Prasad and 6,139,131, both reduced to practice by HP products) demonstrate that the target performance was achievable with the combined teachings.

9. Secondary considerations

None of the usual objective indicia is available on this record to rebut obviousness: no unexpected-results data was submitted (the '246's tables show a smooth, predictable energy/geometry surface, which supports obviousness), no long-felt-unmet-need evidence surfaced, and the commercial-success story is weak (the patent was asserted by an NPE (Slingshot) after two assignments; HP settled IPR2020-01659 before any merits decision, so no finding of validity or non-obviousness ever issued). The one pro-patentee fact is procedural, not substantive: no FWD exists, so no claim has been held obvious — the analysis above is a prediction, not a litigated outcome.

10. Bottom line — claim-by-claim vulnerability to § 103 on the cited art

Practical note for a litigant: the expired patent (adjusted expiration 2024-06-11) limits remedies to pre-expiration conduct, and the IPR's pre-institution settlement leaves no § 315(e) estoppel binding on a new defendant. Prasad (US 6,309,052) and Feinn (US 6,126,277) — the exact references HP assembled — plus HP's own US 6,139,131, are the correct § 103 spearhead for the Group A claims; expect Group C (thin-stack) claims to be the credible core of any validity case the patent owner defends, since the cited art simply does not reach total heater stacks of ≤ ~1100 Å.