Monolithic bragg mirror on germanium image sensor
Patent Information
- Application Number
- CN202522185959.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-16
- Publication Date
- 2026-10-23
- Estimated Expiration
- 2035-10-16
AI Technical Summary
[0002]目前，主流锗图像传感器芯片大多采用倒装焊工艺实现探测器与读出电路(ROIC)的集成，然而倒装焊工艺会导致传感器体积与厚度难以缩减、像素填充因子受限、制造复杂度高且良率偏低、探测信号质量受寄生效应影响等问题，为此，业界进一步提出了单片集成技术方案，该方案通过离子注入及晶圆转移方式，将锗外延层直接集成至ROIC上，并在其上构建全锗PIN探测器结构，其中P区、I区和N区均由锗材料构成，该方案在一定程度上减少了凸点互连带来的局限，实现了探测器与ROIC的单片集成，但仍存在如下技术问题：
[0020]综上，与现有技术相比，本申请实施例提供的技术方案带来的有益效果至少包括：
Smart Images
Figure CN224891039U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of sensor technology, and in particular to a germanium image sensor on a monolithic Bragg mirror. Background Technology
[0002] Currently, most mainstream germanium image sensor chips use flip-chip bonding to integrate the detector and readout circuit (ROIC). However, flip-chip bonding leads to problems such as difficulty in reducing sensor size and thickness, limited pixel fill factor, high manufacturing complexity and low yield, and parasitic effects affecting the quality of the detection signal. To address these issues, the industry has proposed a monolithic integration technology. This solution integrates the germanium epitaxial layer directly onto the ROIC through ion implantation and wafer transfer, and constructs an all-germanium PIN detector structure on top of it. The P-region, I-region, and N-region are all made of germanium. This solution reduces the limitations caused by bump interconnects to some extent and achieves monolithic integration of the detector and ROIC. However, the following technical problems still exist:
[0003] 1. Both the P-region and N-region are fabricated using germanium materials, resulting in insufficient doping efficiency and limited bandgap control, making it difficult to achieve high gain response while maintaining low dark current. 2. To ensure absorption efficiency in the target wavelength band, the all-germanium I-region usually needs to be designed with a large thickness. However, a thick Ge layer is prone to introducing dislocations and interface defects, increasing carrier recombination centers, leading to increased dark current, which in turn affects imaging performance under weak light conditions. 3. This scheme does not introduce an optical enhancement mechanism into the device structure. Photons pass through the absorption layer only once, and unabsorbed photons are directly lost, making it difficult to further improve quantum efficiency.
[0004] In summary, neither the traditional flip-chip bonding process nor the monolithic integrated all-germanium PIN solution can simultaneously meet the comprehensive requirements of germanium image sensor chips for miniaturization, low dark current, and high quantum efficiency. The problem addressed in this application is how to reduce sensor thickness and improve pixel fill factor while suppressing dark current and increasing photon utilization. Summary of the Invention
[0005] This application provides a germanium image sensor on a monolithic Bragg reflector, which can reduce sensor thickness, improve pixel fill factor, suppress dark current, and improve photon utilization.
[0006] This application provides a monolithic germanium image sensor on a Bragg reflector, comprising:
[0007] The readout circuit wafer, Bragg mirror and alumina bonding layer are stacked in sequence, and multiple germanium quantum well pixel modules are disposed on the alumina bonding layer and located on the same horizontal plane.
[0008] The germanium quantum well pixel module includes a doped germanium-silicon contact layer, an intrinsic germanium multi-quantum well absorption layer, and an intrinsic germanium-silicon layer stacked sequentially; the intrinsic germanium-silicon layer has a doped region; the readout circuit wafer has multiple first metal interconnect layers and multiple second metal interconnect layers, and the Bragg mirror has multiple vertical holes.
[0009] The doped regions of each germanium quantum well pixel module are connected to the first metal interconnect layer through vertical holes;
[0010] The doped germanium-silicon contact layer of each germanium quantum well pixel module is connected to the second metal interconnect layer through vertical holes.
[0011] Furthermore, the spacing between each germanium pixel module is the same, and an insulating material is filled between adjacent germanium pixel modules.
[0012] Furthermore, the insulating material is an insulating material, including silicon dioxide or silicon nitride.
[0013] Furthermore, the thickness of the alumina bonding layer is 10 nanometers.
[0014] Furthermore, the germanium-silicon contact layer is either a P-type doped germanium-silicon contact layer or an N-type doped germanium-silicon contact layer.
[0015] Furthermore, the silicon content in the germanium-silicon contact layer is less than or equal to 30%.
[0016] Furthermore, the doped region of the germanium quantum well pixel module is connected to the first metal interconnect layer, and the doped germanium silicon contact layer is connected to the second metal interconnect layer through copper or tungsten metal filled in vertical holes.
[0017] Furthermore, the Bragg reflector includes a first silicon layer and a second silicon layer stacked alternately at a predetermined period.
[0018] Furthermore, the first silicon layer and the second silicon layer are any two materials selected from amorphous silicon, silicon oxide, and silicon nitride.
[0019] Furthermore, the preset cycle is greater than or equal to 3 and less than or equal to 7.
[0020] In summary, compared with the prior art, the beneficial effects of the technical solution provided in this application include at least the following:
[0021] This application provides a monolithic germanium image sensor on a Bragg reflector. First, the integration of the readout circuit wafer and the pixel module adopts a monolithic integration scheme, eliminating the need for bump interconnects or stacked structures, effectively reducing system thickness. Furthermore, the intrinsic germanium multi-quantum-well absorption layer covers the entire pixel module, thereby improving the pixel fill factor, imaging resolution, and detection efficiency. Second, the application uses a doped region of a germanium-silicon contact layer and a doped region of an intrinsic germanium-silicon layer to form the P-region and N-region. The combination of germanium-silicon alloy material and the germanium quantum well structure of the absorption layer enhances junction doping efficiency and bandgap control capability, while effectively suppressing dark current caused by interface defects. Finally, the germanium quantum well structure of the absorption layer can utilize the quantum confinement effect to enhance selective absorption of the target wavelength band, and the thin-layer design reduces defect density, improving response speed and weak-light imaging performance. The Bragg reflector allows photons to travel multiple times within the absorption layer, further improving quantum efficiency and photon utilization. Attached Figure Description
[0022] Figure 1 This is a structural diagram of a germanium image sensor on a monolithic Bragg mirror, provided as an embodiment of this application.
[0023] Figure 2 This is a structural diagram of a germanium image sensor on a monolithic Bragg mirror, provided in another embodiment of this application. Detailed Implementation
[0024] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.
[0025] Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0026] Please see Figure 1 and Figure 2 This application provides a monolithic germanium image sensor on a Bragg mirror, comprising:
[0027] The sequence consists of a readout circuit wafer, a Bragg mirror, and an alumina bonding layer, stacked sequentially, along with multiple germanium quantum well pixel modules disposed on the alumina bonding layer and on the same horizontal plane. The alumina bonding layer is 10 nanometers thick.
[0028] Each germanium pixel module has the same spacing, and an insulating material is filled between adjacent germanium pixel modules.
[0029] The insulating material is an insulating material, which includes silicon dioxide or silicon nitride.
[0030] Specifically, the isolation material can be installed using the shallow trench isolation (STI) process.
[0031] The germanium quantum well pixel module includes a doped germanium-silicon contact layer, an intrinsic germanium multi-quantum well absorption layer, and an intrinsic germanium-silicon layer stacked sequentially; the intrinsic germanium-silicon layer has a doped region; the readout circuit wafer has multiple first metal interconnect layers and multiple second metal interconnect layers, and the Bragg mirror has multiple vertical holes.
[0032] Furthermore, the intrinsic germanium multi-quantum-well absorber layer can also be replaced with an intrinsic germanium-silicon multi-quantum-well absorber layer.
[0033] The doped region is a P-type or N-type doped germanium-silicon contact region, and the doped germanium-silicon contact layer is a P-type doped germanium-silicon contact layer or an N-type doped germanium-silicon contact layer. The silicon content in the doped region and the doped germanium-silicon contact layer is less than or equal to 30%.
[0034] It is worth noting that the doped region and the doped germanium-silicon contact layer are of different types. If the doped region is a P-type doped germanium-silicon contact region, then the doped germanium-silicon contact layer is an N-type doped germanium-silicon contact layer. If the doped region is an N-type doped germanium-silicon contact region, then the doped germanium-silicon contact layer is a P-type doped germanium-silicon contact layer, thus forming the P-region and N-region of the sensor.
[0035] The doped regions of each germanium quantum well pixel module are connected to the first metal interconnect layer through vertical holes.
[0036] The doped germanium-silicon contact layer of each germanium quantum well pixel module is connected to the second metal interconnect layer through vertical holes.
[0037] like Figure 2 As shown, each germanium quantum well pixel module corresponds to a first metal interconnect layer and a second metal interconnect layer. The doped region and the doped germanium silicon contact layer of the germanium quantum well pixel module are connected to the two metal interconnect layers through the Bragg mirror, thereby realizing the connection between the germanium quantum well pixel module and the readout circuit wafer.
[0038] In traditional flip-chip bonding, the detector and ROIC need to be fabricated and stacked separately. The bump interconnect structure increases the system thickness, making it difficult to meet the requirements of portable and miniaturized applications. Furthermore, the bumps in the flip-chip bonding process occupy the pixel area, resulting in insufficient coverage of the photosensitive area, which limits imaging resolution and detection efficiency. In contrast, this application integrates the detector and ROIC on the same wafer platform, eliminating the need for bump interconnects or stacking structures. This effectively reduces the system thickness and significantly improves chip miniaturization and portability. By rationally designing the quantum well absorption layer and pixel layout, the photosensitive area covers the entire germanium quantum well pixel module, thereby improving the pixel fill factor and enhancing imaging resolution and detection efficiency.
[0039] The monolithic germanium image sensor on a Bragg reflector provided in the above embodiments firstly utilizes a monolithic integration scheme for the integration of the readout circuit wafer and the pixel module, eliminating the need for bump interconnects or stacked structures and effectively reducing system thickness. Furthermore, the intrinsic germanium multi-quantum-well absorption layer covers the entire pixel module, thereby improving the pixel fill factor and enhancing imaging resolution and detection efficiency. Secondly, the application employs a doped region of germanium-silicon contact layer and a doped region of intrinsic germanium-silicon layer to form P-regions and N-regions. The combination of germanium-silicon alloy material and the germanium quantum well structure of the absorption layer enhances junction doping efficiency and bandgap control capability, while effectively suppressing dark current caused by interface defects. Finally, the germanium quantum well structure of the absorption layer can utilize the quantum confinement effect to enhance selective absorption of the target wavelength band, and the thin-layer design reduces defect density, improving response speed and weak-light imaging performance. The Bragg reflector configuration enables photons to travel multiple times within the absorption layer, further improving quantum efficiency and photon utilization.
[0040] Understandably, the difference between this application and existing monolithic integrated solutions lies in the improved design of the active region. The core structure of existing solutions is an all-germanium PIN, which requires ion implantation and absorption by a thick germanium layer to achieve detection. This results in problems such as large junction capacitance, high dark current, and limited bandwidth. In contrast, this application introduces a Ge / SiGe multi-quantum-well structure in the absorption region and uses GeSi alloy in the P and N regions to achieve strain and bandgap modulation. This effectively reduces defect recombination and dark current caused by thick absorption while ensuring short-wave infrared response, and significantly improves the signal-to-noise ratio under low illumination.
[0041] In some embodiments, the doped region of the germanium quantum well pixel module is connected to the first metal interconnect layer, and the doped germanium silicon contact layer is connected to the second metal interconnect layer through copper or tungsten metal filled in vertical holes.
[0042] Specifically, vertical vias can be achieved through through-silicon via (TSV) technology, which establishes a vertical interconnect between the detector layer and the readout circuit. The vias formed by TSVs (i.e., the vertical vias of this application) are typically filled with metals such as copper or tungsten to provide a low-resistance path and achieve high-density electrical connection between the pixel electrode and the ROIC metal interconnect layer. This process ensures reliable readout and high-speed signal transmission for large-scale arrays.
[0043] In some embodiments, the Bragg reflector includes a first silicon layer and a second silicon layer stacked alternately at a predetermined period.
[0044] The first silicon layer and the second silicon layer are any two of the following materials: amorphous silicon, silicon oxide, and silicon nitride.
[0045] It can be assumed that the Bragg reflector of this application can be formed by alternating stacks of amorphous silicon layers and silicon oxide layers, alternating stacks of silicon oxide layers and silicon nitride layers, or alternating stacks of amorphous silicon layers and silicon nitride layers.
[0046] The preset cycle is generally greater than or equal to 3 and less than or equal to 7. Figure 1 The example shown uses 5 cycles.
[0047] It is worth noting that existing monolithic integration solutions have not disclosed the synergistic design of MQW + heterojunction + DBR. This application can significantly reduce dark current while maintaining or improving quantum efficiency, thereby obtaining a higher signal-to-noise ratio and better usable imaging sensitivity under weak light conditions. Furthermore, this application can achieve selective enhancement or narrowing of the response to the target SWIR sub-band at the device level by adjusting the well / barrier thickness, strain, and Ge / Si ratio of the MQW, as well as by designing the center wavelength and bandwidth of the DBR, which facilitates the realization of multi-band / spectrally selective sensors.
[0048] In summary, this application achieves a comprehensive breakthrough in miniaturization, low dark current, high quantum efficiency, and process compatibility of short-wave infrared imaging chips through the synergistic effect of heterogeneous structure design in the P-region and N-region, the introduction of a quantum well absorption layer, and the optical enhancement mechanism of a Bragg mirror. This chip can demonstrate excellent performance in various scenarios such as night vision surveillance, environmental perception, remote sensing mapping, semiconductor testing, medical diagnostics, and consumer electronics, providing a new solution for the development of short-wave infrared imaging technology.
[0049] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0050] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.
Claims
1. A germanium image sensor on a monolithic Bragg reflector, characterized in that, include: The readout circuit wafer, Bragg mirror and alumina bonding layer are stacked in sequence, and multiple germanium quantum well pixel modules are disposed on the alumina bonding layer and located on the same horizontal plane. The germanium quantum well pixel module includes a doped germanium-silicon contact layer, an intrinsic germanium multi-quantum well absorption layer, and an intrinsic germanium-silicon layer stacked sequentially; the intrinsic germanium-silicon layer has a doped region; the readout circuit wafer has multiple first metal interconnect layers and multiple second metal interconnect layers; and the Bragg mirror has multiple vertical holes. The doped regions of each of the germanium quantum well pixel modules are connected to the first metal interconnect layer through vertical holes; The doped germanium-silicon contact layer of each of the germanium quantum well pixel modules is connected to the second metal interconnect layer through vertical holes.
2. The germanium image sensor on a monolithic Bragg reflector according to claim 1, characterized in that, Each of the germanium quantum well pixel modules has the same spacing, and an insulating material is filled between two adjacent germanium quantum well pixel modules.
3. The germanium image sensor on a monolithic Bragg reflector according to claim 2, characterized in that, The insulating material is an insulating material, which includes silicon dioxide or silicon nitride.
4. The germanium image sensor on a monolithic Bragg reflector according to claim 1, characterized in that, The thickness of the alumina bonding layer is 10 nanometers.
5. The germanium image sensor on a monolithic Bragg reflector according to claim 1, characterized in that, The germanium-silicon contact layer is either a P-type or an N-type doped germanium-silicon contact layer.
6. The germanium image sensor on a monolithic Bragg reflector according to claim 1, characterized in that, The silicon content in the doped germanium-silicon contact layer is less than or equal to 30%.
7. The germanium image sensor on a monolithic Bragg reflector according to claim 1, characterized in that, The doped region of the germanium quantum well pixel module is connected to the first metal interconnect layer, and the doped germanium-silicon contact layer is connected to the second metal interconnect layer through copper or tungsten metal filled in vertical holes.
8. The germanium image sensor on a monolithic Bragg reflector according to claim 1, characterized in that, The Bragg reflector comprises a first silicon layer and a second silicon layer stacked alternately at a predetermined period.
9. The germanium image sensor on a monolithic Bragg reflector according to claim 8, characterized in that, The first silicon layer and the second silicon layer are any two of the following materials: amorphous silicon, silicon oxide, and silicon nitride.
10. The germanium image sensor on a monolithic Bragg reflector according to claim 8, characterized in that, The preset period is greater than or equal to 3 and less than or equal to 7.