Obviousness

A complete obviousness analysis under 35 U.S.C. § 103 requires access to the full claims of US patent 12243948, which are not provided in the current prompt. However, based on the patent's title, abstract, and detailed "Definitions" section, which describes the general inventive concepts and explicitly cites prior art, a preliminary analysis of potential obviousness can be conducted by hypothesizing typical claim elements.

The patent US12243948, titled "Microstructure enhanced absorption photosensitive devices," generally describes photosensitive devices (photodiodes (PDs), avalanche photodiodes (APDs), photovoltaics (PVs)) that incorporate microstructures such as pillars, holes, and/or voids within their semiconductor absorption regions. These microstructures are designed to enhance photon absorption (e.g., by forming an absorbing mode high contrast grating (HCG) using resonance, scattering, near-field, sub-wavelength, and/or interference effects), reduce capacitance, and extend the device's operating wavelength range, particularly for silicon (Si) at wavelengths like 850 nm and beyond, and for germanium (Ge) and III-V materials.

A person having ordinary skill in the art (PHOSITA) in semiconductor device physics and optical engineering would be motivated to combine various known techniques to improve the performance of photosensitive devices, especially to overcome known limitations such as the trade-off between quantum efficiency (QE) and bandwidth, or the poor absorption of silicon at longer optical wavelengths.

Here are combinations of prior art references (explicitly cited within the patent's "Definitions" section) that would likely render the concepts described in US12243948 obvious:

1. Combining Microstructures for Light Trapping (from Photovoltaics) with Photodiodes/APDs

• Prior Art References:

  • Garnett et al., "Light trapping in silicon nanowire solar cells" (2010): Discloses the use of "silicon nanowires" for "light trapping in photovoltaic applications," experimentally demonstrating a 73-fold increase in optical path length and effective absorption coefficient for silicon nanowire arrays at 850 nm compared to bulk silicon.
  • Kelzenberg et al., "Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications" (2010): Further supports the concept of using "Si wire arrays for photovoltaic applications" to achieve "enhanced absorption and carrier collection".
  • Li et al., "Optical absorption enhancement in silicon nanowire and nanohole arrays for photovoltaic applications" (2010): Explicitly describes "optical absorption enhancement in silicon nanowire and nanohole arrays for photovoltaic applications".

• Motivation for Combination:
  A PHOSITA would be keenly aware of the inherent limitations of conventional silicon photodiodes and avalanche photodiodes, particularly the inverse relationship between bandwidth and quantum efficiency at wavelengths where silicon is weakly absorbing (e.g., 850 nm and longer). To achieve high quantum efficiency, a thick intrinsic ("I") absorption region is typically required, leading to longer carrier transit times and reduced bandwidth (e.g., a 30 µm thick Si "I" layer for 90% absorption at 850 nm limits bandwidth to ~1.5 GHz). Conversely, a thin "I" region for high bandwidth results in low quantum efficiency.

  The cited works by Garnett et al., Kelzenberg et al., and Li et al. clearly demonstrate that micro/nanostructures like nanowires and nanoholes are effective for "light trapping" and "absorption enhancement" in silicon, even at the critical 850 nm wavelength. It would be an obvious design choice for a PHOSITA to apply these proven light-trapping microstructures, already shown to boost absorption in silicon PV cells, to silicon-based photodiodes and avalanche photodiodes. The motivation is directly to overcome the described bandwidth-QE trade-off by achieving high absorption in a physically shorter intrinsic region, thereby maintaining high bandwidth and high quantum efficiency. The patent itself states this problem and solution alignment when it notes that "nanowire is known to be used for light trapping in photovoltaic applications... [but here] the photogenerated carriers are swept out with an external reverse bias in the absorbing 'i' region of a P—I—N diode (PD) or P—I—P—I—N diode (APD) for high modulation bandwidth". While the application (DC PV vs. high-speed PD/APD) differs, the core principle of using microstructures for absorption enhancement in silicon is taught.

• Resulting Obvious Invention: A silicon photodiode or avalanche photodiode incorporating an array of microstructured pillars or holes (analogous to nanowires/nanoholes) in its absorption region, dimensioned to enhance optical absorption and allow for a shorter intrinsic region, thereby achieving high bandwidth (e.g., >10 Gb/s) and high quantum efficiency (e.g., >60%) at wavelengths like 850 nm. The specific dimensions for optimizing performance (e.g., spacing in the "near-wavelength regime" for HCG effects) would be within the realm of routine experimentation or optimization for a PHOSITA familiar with optical resonance phenomena.

2. Combining Ge-on-Si APDs with Microstructured Absorption Enhancement

• Prior Art Reference:

  • Kang et al., "Epitaxially-grown Ge/Si avalanche photodiodes for 1.3 μm light detection" (2008): Describes the fabrication of an "Epitaxially-grown Ge/Si avalanche photodiode" operating at 1310 nm, demonstrating the integration of a Ge absorption layer on a Si multiplication layer. The reported quantum efficiency for a 1 µm thick Ge absorption layer was only 56%.

• Motivation for Combination:
  Kang et al. demonstrates a working Ge-on-Si APD for longer wavelengths but highlights the challenge of achieving high quantum efficiency (only 56% for 1 µm Ge at 1310 nm). A PHOSITA would recognize that to achieve higher QE, either the Ge absorption layer needs to be thicker (which would increase transit time and limit bandwidth) or its absorption efficiency needs to be enhanced. Given the established knowledge of using microstructures to enhance absorption in silicon (from Garnett et al., Li et al.), it would be obvious to extend this approach to a germanium absorption layer, particularly when integrated with silicon. The motivation is to improve the quantum efficiency of Ge-on-Si devices, or enable thinner Ge layers for higher bandwidth, without compromising absorption. The patent itself states this: "Ge on Si microstructures are fabricated on the Ge to increase absorption which allows a shorter length of Ge to be used resulting in higher speed due to lower effective capacitance and shorter transit time for the carriers".

• Resulting Obvious Invention: An epitaxially grown Ge-on-Si avalanche photodiode, similar to that disclosed by Kang et al., where the germanium absorption layer incorporates microstructured pillars or holes to enhance absorption, thereby enabling higher quantum efficiency at 1310 nm (or other long wavelengths) and/or allowing for a thinner Ge layer for increased bandwidth.

3. Incorporating Voids for Refractive Index Modification and Capacitance Reduction

• Prior Art (General Knowledge and Patent's own statements about prior understanding):

  • The patent explicitly states that "microstructures such as voids are used to reduce effective refractive index to create resonant structures to enhance the absorption".
  • It also describes that "structures such as voids, air gaps, and/or holes... have dimensions on the order of the optical wavelength, the optical electromagnetic field will see an average refractive index... referred to herein as the effective refractive index".
  • Furthermore, the patent discusses prior concepts such as "a glass material in which the glass has a plurality of buried voids dimensioned between 0.01 microns to 1000 microns", and a "microwave transmission line structure" with "high-density dielectric-filled voids configured to reduce a dielectric constant of the semiconductor substrate material". An "optical waveguide structure" is also mentioned where a "supporting material includes a plurality of microstructured voids that are configured to alter an effective index of refraction".
  • The patent notes that High Contrast Gratings (HCG) effects, including resonance effects, are generally known (referencing "Chang-Hasnain").

• Motivation for Combination:
  A PHOSITA designing photosensitive devices would understand that optical absorption can be enhanced through resonant structures that control the effective refractive index and optical path. The concept of using voids to modify the effective refractive index of a material and to reduce its dielectric constant (and thus capacitance) is explicitly recognized as known in various technical fields, as indicated by the patent's own background description. Given the desire to enhance absorption (e.g., through resonant HCG structures) and simultaneously reduce device capacitance (to improve high-frequency performance by lowering the RC time constant), it would be an obvious step to incorporate voids into the semiconductor absorption region of a photodetector. The PHOSITA would be motivated to exploit the known effects of voids to achieve these dual benefits.

• Resulting Obvious Invention: A photosensitive device (PD, APD, PV) where the semiconductor absorption region contains a plurality of microstructured voids. These voids would be configured (sized, shaped, density) to reduce the effective refractive index of the region, facilitating resonant absorption enhancement (e.g., by creating HCG effects), and simultaneously reducing the effective capacitance of the device for improved high-frequency operation due to a lower RC time constant.

In summary, while the specific claims are unavailable, the core inventive concepts of US12243948, relating to using microstructures (pillars, holes, voids) to enhance absorption and reduce capacitance in high-speed photosensitive devices across various material systems, appear to be rendered obvious by combining existing knowledge and explicit prior art references, particularly those demonstrating light trapping in similar material systems and the use of voids to modify optical and electrical properties. The motivation for such combinations stems from well-recognized problems in achieving high-performance photosensitive devices.