Seiichi Yoneda

Embedded SRAM and Cortex-M0 core with backup circuits using a 60-nm crystalline oxide semiconductor for power gating

A chip of embedded SRAM having backup circuits using a 60-nm c-axis aligned crystalline oxide semiconductor (CAAC-OS) such as CAAC indium-gallium-zinc oxide (CAAC-IGZO) and Cortex-M0 core having flip-flops with CAAC-OS backup circuits is fabricated. The SRAM and M0 core can retain data using the backup circuits during power-off; thus, they can perform power gating (PG) with backup time of 100 ns and recovery time of 10 clock cycles (including data restoration time (100 ns)). Further, memory cell area and performance in combining a 45-nm Si SRAM memory cell with 60-nm CAAC-OS are estimated to have negligible overhead.

A normally-off microcontroller unit with an 85% power overhead reduction based on crystalline indium gallium zinc oxide field effect transistors

A low-power normally-off microcontroller unit (NMCU) having state-retention flip-flops (SRFFs) using a c-axis aligned crystalline oxide semiconductor (CAAC-OS) such as indium gallium zinc oxide (IGZO) transistors and employing a distributed backup and recovery method (distributed method) is fabricated. Compared to an NMCU employing a centralized backup and recovery method (centralized method), the NMCU employing the distributed method can be powered off approximately 75 µs earlier after main processing and can start the main processing approximately 75 µs earlier after power-on. The NMCU employing the distributed method can reduce power overhead by approximately 85% and power consumption by approximately 18% compared to the NMCU employing the centralized method. The NMCU employing the distributed method can retain data even when it is powered off, can back up data at high speed, and can start effective processing immediately after power-on. The NMCU could be applied to a low-power MCU.

6.5 25.3μW at 60fps 240×160-pixel vision sensor for motion capturing with in-pixel non-volatile analog memory using crystalline oxide semiconductor FET

A vision sensor used to capture motion must operate with very low power when used in sensor networks where power is very limited. Frame-based [1] and event-driven [2,3] vision sensors have been reported. The former captures motion from the difference between captured data of a previous frame and that of a current frame; thus, it is difficult to capture motion of a slowly moving object. An event-driven sensor captures motion of a slowly moving object; however, its pixel configuration is complicated, and it is difficult to perform both motion capturing and image capturing. In this paper, we report a vision sensor for motion capturing having in-pixel non-volatile analog memory utilizing a c-axis aligned crystalline In-Ga-Zn oxide (CAAC-IGZO), a crystalline oxide semiconductor based FET that demonstrates very low off-state current [4] and retains captured data of a given reference frame. Although an electronic global shutter image sensor with improved floating diffusion (FD) charge retention characteristics is reported in [5], our vision sensor realizes normal global shutter and motion capturing depending on the presence or absence of differences with respect to a given reference frame in each pixel. The sensor has 3 modes: an imaging mode to output captured data in pixels, a motion-capturing mode to process differential data using an analog processor, and a standby mode to reduce power after motion capturing for each frame. Power consumption is reduced by operating only circuit blocks needed for each mode. The sensor (240×160 pixels), fabricated by a 0.5μm CAAC-IGZO FET/0.18μm p-channel Si FET (no n-channel Si FET) hybrid process shows power consumption of 25.3μW and 1.88μW at 60fps in the motion-capturing and standby modes, respectively, which equal 1/140th and 1/2000th of the power consumption of the imaging mode.

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Utilizing a c-axis-aligned crystalline oxide semiconductor-based FET, we have fabricated a vision sensor with in-pixel nonvolatile analog memory. The sensor realized normal image data capturing, captured differential data of a given reference frame, and retained the captured data for an extended time in each pixel. Moreover, the sensor realized normal global shutter image capturing and motion capturing by extracting differential images. This is performed using the captured data and depends on the presence or absence of differences between normal images and reference images. The sensor has three operating modes: an imaging mode, a motion capturing mode, and a wait mode. Importantly, power consumption is reduced by powering off circuit blocks that are in a standby state.

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Hitoshi Kunitake, Semiconductor Energy Laboratory Co., Ltd., Japan hk1372@sel.co.jp Shintaro Harada, Semiconductor Energy Laboratory Co., Ltd., Japan Fumika Akasawa, Semiconductor Energy Laboratory Co., Ltd., Japan Yuki Okamoto, Semiconductor Energy Laboratory Co., Ltd., Japan Takashi Nakagawa, Semiconductor Energy Laboratory Co., Ltd., Japan Takeshi Aoki,Seiichi Yoneda, Semiconductor Energy Laboratory Co., Ltd., Japan Hiroki Inoue, Semiconductor Energy Laboratory Co., Ltd., Japan Munehiro Kozuma, Semiconductor Energy Laboratory Co., Ltd., Japan Takayuki Ikeda, Semiconductor Energy Laboratory Co., Ltd., Japan Yoshiyuki Kurokawa, Semiconductor Energy Laboratory Co., Ltd., Japan Shunpei Yamazaki, Semiconductor Energy Laboratory Co., Ltd., Japan