Pixel-Parallel Three-Layer Stacked CMOS Image Sensors Using Double-Sided Hybrid Bonding of SOI Wafers

• Published in: IEEE Transactions on Electron Devices Vol. 70; no. 9; pp. 1 - 7
• Main Authors: Goto, Masahide, Honda, Yuki, Nanba, Masakazu, Iguchi, Yoshinori, Saraya, Takuya, Kobayashi, Masaharu, Higurashi, Eiji, Toshiyoshi, Hiroshi, Hiramoto, Toshiro
• Format: Journal Article
• Language: English; Japanese
• Published: New York IEEE 01.09.2023; Institute of Electrical and Electronics Engineers (IEEE); The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: 3-D integrated circuits; Analog circuits; Analog to digital converters; analog-to-digital converters (ADCs); Bonding; Bonding strength; CMOS; damascene integration; Electrodes; Gold; Image sensors; Internet of Things; Multilayers; Photodiodes; Pixels; Sensor phenomena and characterization; Sensors; Signal processing; Silicon; Silicon dioxide; silicon-on-insulator (SOI); SOI (semiconductors); wafer bonding; Wafers
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2023.3298308

This study reports pixel-parallel three-layer stacked complementary metal-oxide-semiconductor image sensors developed for the first time. The hybrid bonding of silicon-on-insulator (SOI) wafers with Au electrodes embedded in SiO<inline-formula> <tex-math notation="LaTeX">_{\text{2}}</tex-math> </inline-formula> surfaces enabled face-to-back as well as face-to-face bonding, facilitating multilayer stacking, and pixel-parallel signal processing. A three-layered pixel, comprising a photodiode (PD), pulse generation circuit, and counters, served as analog-to-digital converters (ADCs), reducing its size in comparison to conventional two-layered sensors. In addition, wafer bonding introduced a thin Si layer as a bonding medium, thereby ensuring bonding strength and achieving alignment accuracy of less than 1 <inline-formula> <tex-math notation="LaTeX">\boldsymbol{\mu} </tex-math> </inline-formula>m for the entire area of 8-in wafers. The developed three-layered pixel circuit demonstrated a linear response of 16-bit digital signal output. A prototype sensor with a quarter-quarter video graphics array (QQVGA) successfully captured video images. The results revealed the feasibility of multilayered sensors with high-performance characteristics, such as high resolution, high speed, and wide dynamic range, as well as multiple functionalities, including signal processing, memory, and computation. The developed 3-D integration technology can enhance sensor applications, ranging from high-quality video cameras, recognition, automotive systems, robots, and measurements to various Internet-of-Things devices.