Obviousness

Obviousness Analysis under 35 U.S.C. § 103 for US7812505

The present analysis evaluates the obviousness of US Patent 7812505 under 35 U.S.C. § 103, considering combinations of prior art references cited within the patent document. The core of US7812505 lies in a piezoelectric microspeaker (and its manufacturing method) that incorporates a "resonance change unit" to shift resonance frequencies, particularly from an audible to an inaudible band. This unit is described as a patterned structure, often a protrusion, formed by etching the silicon substrate.

Claims of US7812505

The key claims under consideration are:

• Claim 1 (Apparatus): A piezoelectric microspeaker using microelectromechanical systems (MEMS), comprising: a piezoelectric layer disposed on an elastic thin layer; and a resonance change unit patterned on one of a bottom surface of the elastic thin layer and a top surface of the piezoelectric layer.
• Claim 9 (Method): A method of manufacturing a piezoelectric microspeaker using MEMS, comprising: forming an elastic thin layer, a piezoelectric layer, and an electrode over a first surface of a silicon substrate; and forming a pattern over a second surface of the silicon substrate, the second surface being on an opposing side of the first surface, the pattern being configured to change a resonance frequency.

Dependent claims further specify materials, layering, bonding, etching techniques, and the purpose of the resonance change unit.

Prior Art Combinations and Motivation for Obviousness

A person having ordinary skill in the art (POSITA) in the field of MEMS piezoelectric transducers, seeking to address known challenges such as undesirable resonance frequencies in the audible band, would have found the claimed inventions obvious in light of the following combinations of prior art:

Combination for Claims 1, 6, and 7 (Apparatus and related features)

• Primary References: US20030048914A1 (Yi), US6924584B2 (Palo Alto Research Center Inc.).
• Secondary Reference: WO2007078646A1 (Intel Corporation).

1. Known MEMS Piezoelectric Microspeakers: Yi teaches a micromachined piezoelectric microspeaker and its fabrication, including a piezoelectric layer formed on a diaphragm (elastic thin layer) over a silicon substrate. Eunki Hong et al. similarly describe micromachined piezoelectric diaphragms with a PZT thin film on a silicon diaphragm.
2. Concept of Resonance Tuning/Frequency Control: Yi explicitly mentions "tuning a resonance frequency to a desired frequency" to achieve "uniform acoustic characteristics" by forming "sound emitting holes" in the diaphragm. While these are holes, they represent patterned features on the diaphragm designed to modify resonance. Palo Alto Research Center discloses piezoelectric transducers where diaphragms have "features which affect the mechanical response of the transducers to achieve frequency selective operation," utilizing "multiple sub-diaphragms" defined by "etched regions." This directly teaches patterning a diaphragm to control its frequency response. Intel's patent further reinforces the general concept of "frequency tuning" in film bulk acoustic resonators (FBARs) by "modifying a mass of the resonator by adding or subtracting material" or "modifying a stress in the resonator."
3. Motivation to Combine: The background of US7812505 itself highlights the problem of "a plurality of resonance frequencies are included in an audible frequency band." A POSITA, aware of this problem and the teachings of Yi and Palo Alto Research Center regarding diaphragm patterning for resonance tuning/frequency selection, would be motivated to combine these approaches. Knowing that modifying the mass and/or stiffness of a vibrating diaphragm alters its resonance frequencies (as supported by Intel), a POSITA would find it obvious to implement a patterned structure, such as a localized protrusion (resonance change unit), on the bottom surface of the elastic thin layer (which forms part of the diaphragm assembly). This protrusion, by locally varying the mass and stiffness, would shift the resonance frequencies. The specific placement "on the bottom surface of the elastic thin layer" would be a matter of routine design choice to achieve the desired mechanical modification and manage fabrication. Claim 7, which specifies patterning to change resonance frequency from an audible to an inaudible band, describes a desired outcome that would be an obvious objective for a POSITA applying known frequency tuning techniques to address the stated problem.

Combination for Claims 9, 8, 12, and 13 (Method and related features)

• Primary References: US20030048914A1 (Yi), US6924584B2 (Palo Alto Research Center Inc.).
• Secondary Reference: General knowledge of MEMS fabrication techniques.

1. Standard MEMS Manufacturing: Yi teaches a method of manufacturing a micromachined piezoelectric microspeaker involving depositing layers (e.g., elastic thin layer, piezoelectric layer, electrode) on a silicon substrate. Yi also details etching the silicon substrate from the rear surface (opposing side) to create a back cavity, allowing the diaphragm to vibrate. This establishes the foundational steps of Claim 9.
2. Patterning by Etching for Resonance Control: Palo Alto Research Center teaches that "etched regions define the sub-diaphragms" which are used for "frequency selective operation" by affecting the mechanical response of the transducer.
3. Motivation to Combine: A POSITA manufacturing MEMS piezoelectric microspeakers, following known processes like those in Yi, would perform backside etching of the silicon substrate. Recognizing the need to control resonance frequencies (as described in Yi and the background of US7812505), and having the knowledge from Palo Alto Research Center that patterning by etching can achieve such control, the POSITA would be motivated to modify the standard backside etching step. This modification would involve creating a specific pattern (e.g., a protrusion, which the patent itself describes as "leaving the silicon during the etching of the silicon substrate") on the opposing surface of the silicon substrate. This pattern would then act to change the resonance frequency, fulfilling the purpose of the claimed invention.
4. Etching Techniques (Claims 8, 12): The use of Deep Reactive Ion Etching (DRIE) or anisotropic Si etching (e.g., KOH wet etching) for patterning silicon substrates in MEMS is well-established and represents routine choices for a POSITA. US7812505 itself states that the resonance change unit can be patterned using DRIE or anisotropic Si etching and that the silicon substrate can be etched using DRIE or KOH wet etching.
5. Multiple Etching Steps (Claim 13): US7812505 acknowledges that "the nonuniformity of the silicon substrate ... greatly affects the sound quality ... etching ... may be performed twice or three times." Multi-step etching processes are known in MEMS to improve uniformity, achieve complex geometries, or control etch depth, especially when precision is critical for device performance. A POSITA facing known issues of non-uniformity in etching, particularly for an acoustically sensitive device, would find it obvious to employ multiple etching steps to mitigate this problem and improve acoustic quality.

Obviousness of Dependent Claims (2, 3, 4, 5, 10, 11)

These claims describe specific materials, layer structures, and fabrication details that are generally known and conventional in the MEMS piezoelectric transducer art:

• Claim 2 (Elastic thin layer material): Silicon, silicon oxide, or silicon nitride. Yi, Palo Alto Research Center, and Eunki Hong et al. all teach these materials for diaphragms.
• Claim 3 (Piezoelectric layer bonding/deposition): Bonding with epoxy adhesive or sol-gel deposition. Intel mentions sol-gel deposition for piezoelectric materials. Epoxy adhesives are also commonly used for bonding in MEMS.
• Claim 4 (Piezoelectric layer single material): PZT, PMN-PT, PVDF, ZnO, AlN, lead-free. Yi and Palo Alto Research Center both teach the use of PZT, ZnO, and PVDF.
• Claim 5 (Piezoelectric layer multiple-layer structure): Including Ti, Pt, PZT, and Pt layers. This is a common and well-known electrode and piezoelectric material stack in PZT thin-film MEMS fabrication.
• Claim 10 (Method with lower electrode, insulating layer, upper electrode): This describes a standard architecture for piezoelectric microspeakers with upper and lower electrodes, as generally shown in Yi and FIG. 1 of US7812505 itself.
• Claim 11 (Method with adhesive, piezoelectric layer, interdigitated electrode): Eunki Hong et al. explicitly describes "micromachined piezoelectric diaphragms actuated by ring shaped interdigitated transducer electrodes" with PZT thin films on silicon diaphragms. The use of an adhesive for bonding piezoelectric layers is also a known technique.

Conclusion

Based on the analysis of the cited prior art, all claims of US7812505 would likely be found obvious to a POSITA. The concept of using patterned structures to modify resonance frequencies in MEMS piezoelectric transducers was known. The specific implementation of a "resonance change unit" as a patterned protrusion formed by etching the silicon substrate is an obvious variation and combination of existing techniques and motivations in the field of MEMS acoustic devices. The materials, fabrication methods, and layer structures described in the dependent claims are also widely disclosed or represent routine engineering choices within the art.