US 6634770

Here's a concise summary of US patent 6634770:

US Patent 6634770: Light source using semiconductor devices mounted on a heat sink

• Title: Light source using semiconductor devices mounted on a heat sink
• Current Assignee: Cao Lighting Inc
• Inventor: Densen Cao
• Filing Date: 2001-08-24
• Issue Date: 2003-10-21
• Abstract: A semiconductor light source for illuminating a physical space has been invented. In various embodiments of the invention, a semiconductor such as an LED chip, laser chip, LED chip array, laser array, an array of chips, or a VCSEL chip is mounted on a heat sink. The heat sink may have multiple panels for mounting chips in various orientations. The chips may be mounted directly to a primary heat sink which is in turn mounted to a multi-panel secondary heat sink. A thermoelectric (TE) cooler and air circulation may be provided to enhance heat dissipation. An AC/DC converter may be included in the light source fitting.

Plain-Language Overview of Independent Claims:

• Independent Claim 1: This claim describes a semiconductor light source designed to emit white light for illuminating spaces used by humans. It comprises an enclosure made of a material transparent to white light, mounted on a base. Inside the enclosure, there's a secondary heat sink, and multiple smaller primary heat sinks are mounted on it. A semiconductor chip (such as an LED, LED array, laser chip, or VCSEL chip) is mounted on one of these primary heat sinks, emitting monochromatic light. This chip includes a substrate with specific epitaxial layers: a buffer layer (to reduce material differences), a first cladding layer (to confine electrons), an active layer (which emits light), a second cladding layer (sandwiching the active layer), and a contact layer for electrical connection. Crucially, the device also includes a coating that converts the monochromatic light from the chip into white light.
• Independent Claim 13: This claim also describes a semiconductor light source intended to create white light for illuminating human-occupied spaces. It features an enclosure made of a material transparent to white light, enclosing an interior volume. Within this volume, there is a heat sink designed to dissipate heat from one or more semiconductor devices. Each of these semiconductor devices is capable of emitting light and includes a substrate with a buffer layer, a first cladding layer, an active layer (for light emission), a second cladding layer (surrounding the active layer), and a contact layer for power.

Litigation Information (as of April 26, 2026):

The patent US6634770 is listed as "Expired - Lifetime" with an expiration date of 2021-12-14.

While a search for specific US6634770 dockets in CAFC for 2026 did not yield direct results in the publicly available scheduled cases, the patent record indicates that there were US cases filed in the Court of Appeals for the Federal Circuit in 2024 related to this patent (cases 24-1222 and 24-1223). The status of these 2024 cases in 2026 is not immediately ascertainable from the provided scheduled case lists.

Known litigation involving US patent 6634770 includes the following cases:

1. PTAB Case IPR2022-00848

   • Plaintiff(s): Wolfspeed, Inc. et al. (Petitioner)
   • Defendant(s): CAO Lighting, Inc. et al. (Patent Owner)
   • Jurisdiction: PTAB (Patent Trial and Appeal Board)
   • Case Number: IPR2022-00848
   • Filing Date: April 7, 2022 (Petition filed)
   • Outcome/Current Status: A Final Written Decision was issued. The specific finding of the Final Written Decision (e.g., whether claims were invalidated) is not available from the provided snippets.

2. CAO Lighting, Inc. v. General Electric Company et al.

   • Plaintiff(s): CAO Lighting, Inc.
   • Defendant(s): General Electric Company, Consumer Lighting (U.S.), LLC d/b/a GE Lighting, and Current Lighting Solutions, LLC
   • Jurisdiction: U.S. District Court for the District of Delaware
   • Case Number: C.A. No. 1:20-cv-00681-GBW
   • Filing Date: 2020
   • Outcome/Current Status: A jury verdict was entered on February 17, 2023, and the case is currently stayed.

3. CAO Lighting, Inc. v. Cree, Inc. et al.

   • Plaintiff(s): CAO Lighting, Inc.
   • Defendant(s): Cree, Inc. et al. (including Cree Lighting dba Ideal Industries Lighting)
   • Jurisdiction: United States District Court for the Middle District of North Carolina
   • Case Number: C.A. No. 1:21-cv-00634
   • Filing Date: August 2021 (specifically, August 12, 2021)
   • Outcome/Current Status: The dispute was favorably settled and dismissed prior to the deadline to file a Preliminary Response.

4. CAO Lighting, Inc. v. Wolfspeed, Inc., et al.

   • Plaintiff(s): CAO Lighting, Inc.
   • Defendant(s): Wolfspeed, Inc., et al.
   • Jurisdiction: U.S. Court of Appeals for the Federal Circuit
   • Case Number: Appeal Nos. 2024-1194, 2024-1221, 2024-1222, 2024-1223
   • Filing Date: The appeal numbers indicate filings in 2024.
   • Outcome/Current Status: Judgment was entered on September 5, 2025. A request for panel review and en banc review was denied on November 6, 2025, and the mandate was issued on November 13, 2025.

Proceedings overview

There is one AIA trial proceeding on file for US patent 6634770, which is an Inter Partes Review (IPR) that has reached a Final Written Decision. The IPR resulted in the cancellation of several claims, while others were found patentable. This gives a defendant a stronger defensive posture against certain claims of the patent.

IPR2022-00848 — Unified Patents, LLC v. Cao Lighting Inc.

• Type: Inter Partes Review
• Filed: 2022-05-19 (Petition Filing Date as per Unified Patents)
• Status: Final Written Decision issued (claims canceled and claims sustained)
• Judge panel: Not publicly available in the provided snippets.
• Petition grounds: Not explicitly detailed in the provided snippets, but likely based on obviousness and/or anticipation under 35 U.S.C. §§ 102 and/or 103, as is common for IPRs.
• Institution decision: Instituted. The specific reasoning for institution is not provided in the snippets, but the case proceeded to a Final Written Decision, indicating institution occurred.
• Final Written Decision: The full details of the Final Written Decision are not provided in the snippets. However, the "Proceedings overview" statement indicates that "several claims" were cancelled, and "others were found patentable."
• Settlement / termination: Not indicated in the provided snippets.
• Appeal: Not indicated in the provided snippets.
• Defensive value: This proceeding indicates that some claims of US6634770 have been cancelled, meaning any infringement theory relying solely on these cancelled claims would be significantly weakened or invalid. Conversely, claims found patentable remain valid and could still form the basis of an infringement assertion.

Strategic summary

The patent US6634770 has been subjected to at least one IPR proceeding (IPR2022-00848). This IPR resulted in a mixed outcome, with "several claims" being cancelled and "others" being sustained. Without the specific claim-by-claim breakdown from the Final Written Decision, it is not possible to definitively list which claims are cancelled versus sustained. However, it is clear that the patent's scope has been narrowed. Claims not challenged in IPR2022-00848, or those challenged but upheld, remain active.

Regarding the estoppel landscape, Unified Patents, LLC, and any parties in privity with them, are estopped under 35 U.S.C. § 315(e)(2) from asserting invalidity grounds in future proceedings that they raised or reasonably could have raised during IPR2022-00848. For other potential defendants, prior art grounds not addressed in this IPR may still be available. The fact that Unified Patents, an entity known for defensive IPR filings, was the petitioner, suggests a strategic effort to challenge the patent's validity.

Recommended next steps

As a defendant, it is crucial to obtain and thoroughly review the Final Written Decision for IPR2022-00848 to understand precisely which claims of US6634770 were cancelled and which were sustained. The decision can be found on the USPTO PTAB Decisions portal by searching for IPR2022-00848. The disposition of the claims will directly impact any assertion against you. If the claims cited in a demand letter are among those cancelled, this provides a strong basis for defense.

There are no active PTAB proceedings indicated in the provided data beyond the concluded IPR2022-00848.

Inventors

• Densen Cao (Individual) - No employer specified at the time of filing. The patent lists "Individual" as the original assignee, implying Densen Cao was the original applicant and inventor.

Original assignee

The original assignee on the issued patent US6634770B2 was "Individual". According to Google Patents, the original assignee was "Individual" and then "CAO GROUP, INC." in 2001. CAO Group, Inc. was founded by Densen Cao, the inventor.

Their primary line of business appears to be in lighting and dental technology, based on later assignee names like "Cao Lighting Inc" and the inventor's history. It's unclear if they shipped products embodying the claims at the time of the patent's filing.

Current Status: CAO Group, Inc. appears to be still operating, specializing in dental products. Cao Lighting Inc is also listed as a current assignee on Google Patents.

Assignment timeline

• 2001-08-24 (executed) / recorded 2001-08-24
  • Conveyance: Assignment
  • Assignor: Densen Cao
  • Assignee: CAO GROUP, INC.
  • Correspondent: Not specified in Google Patents.
  • Context: Inventor assigned rights to their company.
• 2015-10-02 (executed) / recorded [DATE NOT SPECIFIED]
  • Conveyance: Assignment
  • Assignor: CAO GROUP, INC.
  • Assignee: EPISTAR CORPORATION
  • Correspondent: Not specified in Google Patents.
  • Context: Transfer to a known LED manufacturer.
• 2015-10-06 (executed) / recorded [DATE NOT SPECIFIED]
  • Conveyance: Corrective Assignment
  • Assignor: CAO GROUP, INC.
  • Assignee: EPISTAR CORPORATION
  • Correspondent: Not specified in Google Patents.
  • Context: Corrective assignment to update assignee address.
• 2016-10-25 (executed) / recorded [DATE NOT SPECIFIED]
  • Conveyance: Assignment
  • Assignor: EPISTAR CORPORATION
  • Assignee: CAO GROUP, INC.
  • Correspondent: Not specified in Google Patents.
  • Context: Patent assigned back to the original company.
• 2016-10-26 (executed) / recorded [DATE NOT SPECIFIED]
  • Conveyance: Assignment
  • Assignor: CAO GROUP, INC.
  • Assignee: CAO LIGHTING, INC.
  • Correspondent: Not specified in Google Patents.
  • Context: Internal reorganization / transfer to a subsidiary focused on lighting.

Timeline diagram

timeline
    title Ownership of US 6634770
    2001 : Assigned to CAO GROUP, INC.
    2003 : Issued
    2015 : Assigned to EPISTAR CORPORATION
         : Corrective Assignment
    2016 : Assigned to CAO GROUP, INC.
         : Assigned to CAO LIGHTING, INC.

NPE / troll-pattern signals

1. Shell-entity transfer — unclear. While "CAO LIGHTING, INC." could potentially be a licensing-focused entity, there's no immediate evidence like a registered-agent address or lack of products to definitively classify it as a shell. It is a subsidiary of the original assignee.
2. Known asserter in the chain — not present. Epistar Corporation is a known LED manufacturer, not typically identified as an NPE. Cao Group and Cao Lighting are also operating companies.
3. Repeat correspondent across the chain — unclear. The Google Patents record does not provide correspondent information for the assignments. A USPTO Assignment Search would be needed to confirm this.
4. Cascading transfers — present. There are three assignments occurring within a 13-month period: "CAO GROUP, INC. to EPISTAR CORPORATION" (October 2, 2015), "EPISTAR CORPORATION to CAO GROUP, INC." (October 25, 2016), and "CAO GROUP, INC. to CAO LIGHTING, INC." (October 26, 2016). This rapid succession, particularly the transfer out and then back in, and then to a related entity, is notable.
5. Pre-litigation transfer — unclear. Litigation related to this patent is mentioned on Google Patents, with the first worldwide family litigation filed and PTAB case IPR2022-00848 filed in 2022. The most recent assignment was in October 2016, which is more than 6 months before 2022, so this particular signal is not strongly present based on the information available. However, a comprehensive litigation history check would be required to definitively confirm the exact date of the first infringement suit involving this patent.
6. Bankruptcy fire-sale — not present. There is no indication of bankruptcy for CAO Group, Inc. or Epistar Corporation in the provided data.
7. Privateering — unclear. The transfer to Epistar and then back to Cao Group, and subsequently to Cao Lighting, could potentially indicate a strategic maneuver, but there's no explicit evidence of an assertion agreement or SEC filings to confirm privateering.
8. Defensive aggregator (anti-NPE) — not present. The chain does not terminate at any known defensive aggregators like RPX, AST, LOT Network, Unified Patents, or Open Invention Network.

Verdict

Insufficient data. While there are cascading transfers (October 2015 to October 2016) which could be a signal for NPE activity, the lack of correspondent information and definitive evidence on the nature of Cao Lighting Inc. as a shell entity prevents a high-confidence determination. Further investigation using the USPTO Assignment Center, including correspondent details and a full litigation history, would be needed for a more conclusive verdict. (USPTO Assignment Center search page: https://assignmentcenter.uspto.gov/)

To identify the most relevant prior art for US patent 6634770, I will search the USPTO database for the patent and then examine its cited references.

It's important to note that "prior art" in the context of patent examination generally includes any evidence that an invention is already known. This can include previously granted patents, published patent applications, scientific literature, and even public use or sale of an invention before the patent's critical date. For this task, I will focus on prior art citations listed within the patent document itself.

Here's the analysis of the prior art cited in US6634770:

Most Relevant Prior Art for US Patent 6634770

US patent 6634770, titled "Light source using semiconductor devices mounted on a heat sink," cites three US patents as prior art in its "BACKGROUND OF INVENTION" section. These references highlight the existing state of LED technology and its limitations prior to the invention described in US6634770.

1. U.S. Pat. No. 5,941,626

   • Full Citation: U.S. Pat. No. 5,941,626
   • Publication/Filing Date: The patent text only provides the publication number. However, Google Patents lists its publication date as August 24, 1999, and its filing date as February 20, 1998.
   • Brief Description: This patent discloses a "long light emitting apparatus that uses a plurality of LED lamps (modules) connected in series." The LED modules are spaced apart and are described as being intended for decorative use, such as on street lamp poles and Christmas trees.
   • Potentially Anticipates (35 U.S.C. § 102): This reference potentially anticipates aspects of US6634770 related to the use of multiple LED lamps in a light-emitting apparatus, particularly if the claims broadly cover such an arrangement without specific limitations related to high-power illumination or heat dissipation. However, US6634770 distinguishes itself by focusing on high-power illumination for physical spaces and efficient heat dissipation, which this prior art explicitly lacks due to its decorative purpose.
     • Specific Claims: Without a detailed claim analysis, it's difficult to pinpoint exact anticipation. However, it could be relevant to broader interpretations of Claim 1, which generally recites "a semiconductor light source for emitting light to illuminate a space used by humans... a plurality of primary heat sinks mounted on said secondary heat sink... a semiconductor chip capable of emitting light mounted on one of said primary heat sinks." The key distinction for US6634770 likely lies in the high power aspect and efficient heat dissipation for general illumination, which this prior art does not address.

2. U.S. Pat. No. 5,160,200

   • Full Citation: U.S. Pat. No. 5,160,200
   • Publication/Filing Date: The patent text only provides the publication number. However, Google Patents lists its publication date as November 3, 1992, and its filing date as March 6, 1991.
   • Brief Description: This patent discloses a "wedge-base LED bulb housing." It depicts "a plurality of separate LED modules electrically connected to a wedge base."
   • Potentially Anticipates (35 U.S.C. § 102): This reference could be relevant to aspects of US6634770 that involve mounting LED modules within a bulb housing with a standard base. However, the distinction in US6634770 lies in the specific "high power" nature of the LEDs, the intricate heat sink design, and the overall goal of efficiently illuminating physical spaces, rather than merely providing an LED bulb housing.
     • Specific Claims: This could potentially relate to elements of Claim 1 concerning "an enclosure," "a base to which said enclosure is mounted," and the general concept of semiconductor devices in a light source. Claim 2, which specifically mentions a "power module... including a fitting for installation in a traditional light bulb socket," could also be considered in light of this prior art, with distinctions being drawn on the specific power conversion and high-power aspects of US6634770.

3. U.S. Pat. No. 4,675,575

   • Full Citation: U.S. Pat. No. 4,675,575
   • Publication/Filing Date: The patent text only provides the publication number. However, Google Patents lists its publication date as June 23, 1987, and its filing date as July 13, 1984.
   • Brief Description: This patent discloses "light-emitting diode assemblies such as a mono-color or bi-color light string system." Each LED is in an envelope with light conducting optical spheres for light transmission and dispersion. This LED string system also appears adapted for decorative use, such as for lighting Christmas trees.
   • Potentially Anticipates (35 U.S.C. § 102): Similar to U.S. Pat. No. 5,941,626, this reference could anticipate broad aspects of using multiple LEDs for illumination. However, its stated purpose is decorative, and it does not address the challenges of high-power illumination or efficient heat dissipation that US6634770 aims to solve. The "light conducting optical spheres" are also a different approach to light management compared to the heat sink and coatings described in US6634770.
     • Specific Claims: Again, without a more granular analysis, it could broadly relate to Claim 1's mention of "semiconductor devices being capable of emitting light." However, the "coating for converting monochromatic light emitted by said chip to white light" and the extensive heat dissipation structures in US6634770 would likely distinguish it.

The overall theme from these cited prior art references is that while LEDs were known and used for various lighting applications (particularly decorative and indicator lights), the prior art did not effectively address the challenges of using high-power LEDs for general space illumination, especially concerning efficient heat dissipation and producing white light. US6634770 aims to bridge this gap.

Obviousness Analysis of US6634770 under 35 U.S.C. § 103

A patent claim is considered obvious under 35 U.S.C. § 103 if "the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains." This analysis involves determining the scope and content of the prior art, identifying the differences between the prior art and the claimed invention, and ascertaining the level of ordinary skill in the pertinent art. A person of ordinary skill in the art (PHOSITA) is a hypothetical person presumed to know the relevant art at the time of the invention and possess ordinary creativity.

The filing date of US6634770 is August 24, 2001.

Level of Ordinary Skill in the Art

In the field of light sources using semiconductor devices, a PHOSITA would likely possess a strong understanding of electrical engineering, semiconductor physics, and thermal management principles. They would be familiar with the operation and fabrication of LEDs, laser diodes, and VCSELs, as well as common packaging and heat dissipation techniques for electronic components. This would include knowledge of different substrate materials, epitaxial layer growth, electrical contacts, and the use of phosphors for wavelength conversion.

Potential Combinations of Prior Art

The patent US6634770 lists several prior art references, which can be analyzed for obviousness in combination with other general knowledge in the field.

Prior Art References:

• U.S. Pat. No. 5,941,626 (hereinafter "626 patent"): Discloses a long light-emitting apparatus using a plurality of LED lamps (modules) connected in series, primarily intended for decorative use.
• U.S. Pat. No. 5,160,200 (hereinafter "200 patent"): Discloses a wedge-base LED bulb housing, depicting multiple separate LED modules electrically connected to a wedge base.
• U.S. Pat. No. 4,675,575 (hereinafter "575 patent"): Discloses light-emitting diode assemblies such as mono-color or bi-color light string systems, with each LED in an envelope with light-conducting optical spheres for transmission and dispersion. Also appears adapted for decorative use.

Combination 1: US 5,160,200 + General Knowledge of Heat Dissipation and Phosphor Coatings

Claim Elements Addressed: Independent Claims 1 and 13, particularly the features related to mounting semiconductor chips on heat sinks, using multiple semiconductor devices, and converting monochromatic light to white light.

The "200 patent" discloses a wedge-base LED bulb housing with a plurality of separate LED modules electrically connected to a wedge base. While the "200 patent" itself does not explicitly detail heat sinks for high-power applications or wavelength conversion coatings, a PHOSITA would recognize the inherent heat generation in LED devices, especially when used in arrays or for illumination purposes.

Motivation for Combination:

1. Heat Dissipation: It would have been obvious to a PHOSITA at the time of the invention to incorporate heat dissipation mechanisms in LED light sources, particularly for "high power" applications where LED output is greater than 40 milliwatts, as acknowledged in the specification of US6634770. The "200 patent" teaches multiple LED modules in a bulb housing. LEDs generate heat, and effective heat dissipation is crucial for their performance and longevity. Materials like copper and aluminum were well-known for their high thermal conductivity and use in heat sinks. Therefore, incorporating a heat sink (secondary and primary, as described in US6634770) in conjunction with the LED modules of the "200 patent" to draw heat away from the semiconductor devices would have been a predictable design choice to improve performance and lifespan.
2. Wavelength Conversion to White Light: The "200 patent" describes LED modules. At the time of the invention, generating white light from monochromatic LEDs (e.g., blue LEDs) using phosphor coatings was a known technique in the art. The specification of US6634770 itself describes that "the interior surface 101 b maybe covered with a phosphor coating to convert blue light into white light" and references "YAG:Ce or other phosphor powders or coatings" as examples of luminous powder coatings. Given the objective of illuminating physical spaces with visible light (as articulated in US6634770), a PHOSITA would have been motivated to apply such a known wavelength-modifying coating to the LED modules of the "200 patent" to achieve white light output. This would be a straightforward application of known technology to achieve a desired and predictable result in an LED illumination device.

Combination 2: US 5,941,626 + US 5,160,200 + General Knowledge of Semiconductor Device Packaging

Claim Elements Addressed: Independent Claims 1 and 13, particularly the arrangement of multiple semiconductor devices, mounting on heat sinks, and the overall structure of a semiconductor light source for illumination.

The "626 patent" discloses a plurality of LED lamps (modules) connected in series in a long light-emitting apparatus. The "200 patent" discloses a wedge-base LED bulb housing containing a plurality of separate LED modules.

Motivation for Combination:

1. Adapting Decorative LED Arrays for General Illumination: Both the "626 patent" and the "575 patent" are described as being primarily for decorative use. The "626 patent" uses spaced-apart LED modules for decorative purposes. The "200 patent" shows multiple LED modules in a bulb housing. A PHOSITA, seeking to overcome the limitations of prior art semiconductor light sources not being successfully and economically used to illuminate physical spaces (as stated in the background of US6634770), would have been motivated to combine the concept of multiple LED modules (from both the "626" and "200" patents) into a more compact and efficiently cooled structure suitable for general illumination.
2. Integration of Heat Sinks: As discussed in Combination 1, the need for heat dissipation in multi-LED systems would have been evident. Combining the multiple LED modules described in the "626 patent" (or even the "200 patent") with the heat sink structures detailed in US6634770 (e.g., primary and secondary heat sinks, perhaps with cooling enhancements like TE coolers and fans) would be a logical step for a PHOSITA to enable higher power output and longer lifespan for general illumination applications. The background of US6634770 explicitly states that "arranging a sufficient number of prior art LED modules to generate high light intensity... took an excessive amount of physical space and created unmanageable amounts of heat," directly pointing to the motivation to improve heat management in multi-LED systems.
3. Application of Epitaxial Layer Structures: The detailed epitaxial layer structures for LEDs and VCSELs, including buffer layers, cladding layers, active layers, and contact layers, were well-known in the semiconductor industry prior to the filing date of US6634770. These are fundamental aspects of LED and VCSEL fabrication. A PHOSITA would understand that the semiconductor devices in the "626" and "200" patents would inherently comprise such structures to function as light-emitting devices. Therefore, explicitly describing these known internal structures within the context of a combined LED light source would not render the overall combination non-obvious.

In summary, the core inventive concept of US6634770 revolves around using semiconductor devices (LEDs, lasers) on heat sinks for general illumination, often with wavelength conversion to white light. The prior art demonstrates the use of multiple LEDs in various configurations and the basic principles of LED construction. The integration of efficient heat dissipation and wavelength conversion, while specific in their implementation in US6634770, represent predictable design choices and combinations of known elements that a person of ordinary skill in the art would have been motivated to make to improve the performance and applicability of LED lighting for general illumination.