World's First LSI with OS and Silicon Hybrid-Structure
Infinite Potential of Crystalline Oxide Semiconductor (OS)


Application of Crystalline OS to Memory, CPU, and FPGA

The combination of silicon LSI and a Crystalline OS FET (OSFET®) with extremely low off-state current characteristics realizes the development of non-conventional devices. Our OS/Si hybrid LSI structure where Crystalline OS is stacked on a silicon CMOS circuit can open up a way to evolve silicon LSI electronic devices into low-power consuming electronic devices.
The extremely low off-state current of OSFET® can realize super low power of electronic devices such as nonvolatile memory, CPU, FPGA, and image sensor.


DOSRAM®

(Dynamic Oxide Semiconductor Random Access Memory)

Super-low-power device enabled by significantly reducing refresh operations


DOSRAM is based on DRAM and has a memory cell that consists of one transistor and one capacitor like DRAM.
With the use of OSFETs, DOSRAM can realize high speed operation and reduce the refresh rate to several times per hour to several times per year, whereas conventional DRAM needs refresh operations with the interval of milliseconds or less.
Moreover, the OS/Si hybrid structure enables stacking of a sense amplifier array and a DOSRAM cell array, thereby reducing energy for data writing/reading[1].

[1] T. Onuki et al., “Embedded Memory and ARM Cortex-M0 Core Using 60-nm C-Axis Aligned Crystalline Indium-Gallium-Zinc Oxide FET Integrated with 65-nm Si CMOS”, IEEE Symp. VLSI Circuits Dig. Tech. Pap., 125 (2016).



NOSRAM®

(Non-volatile Oxide Semiconductor Random Access Memory)

Memory with potentially limitless writing cycles

This is a new voltage-controlled nonvolatile memory that utilizes the extremely low off-state current of OSFET®. This memory achieves unlimited writing cycles and high-speed writing of multi-level data at low power.

In a NOSRAM cell, data is stored by holding a charge (see the lower right figure). For this structure, more information can be stored in a single cell by suppressing variations between elements and finely controlling the writing voltage. SEL developed a 4bit-per-cell NOSRAM in 2014, and now SEL has achieved 6 bits per cell (64 levels) with a voltage distribution width of 25 mV, demonstrating a possibility for a never-before-seen high-density memory device.

nosram

[1] Demonstrated at “Display Innovation 2014”, October 29 to 31, 2014, Pacifico Yokohama, Japan.
[2] T. Matsuzaki et al., “A 128kb 4b/cell Nonvolatile Memory with Crystalline In-Ga-Zn Oxide FET Using Vt Cancel Write Method”, IEEE Int. Solid-State Circuits Conf. Dig. Tech. Pap., 125 (2015).



FPGA

(Field Programmable Gate Array)

Reconfigurable logic circuit with no need for wire reconnection at each time of power-on

FPGA is an integrated circuit where the user can change the connection of internal wiring. Since NOSRAM is used to store the connection configurations of the wires, there is no need to reconnect the wires when the power is turned on, unlike typical FPGA[3].

FPGA

[3] Y. Okamoto, “Novel Application of Crystalline Indium-Gallium-Zinc-Oxide Technology to LSI: Dynamically Reconfigurable Programmable Logic Device Based on Multi-Context Architecture”, ECS Trans., 54 (1) 141, (2013).



32-Bit NoffCPU®

(32-Bit Normally-Off Central Processing Unit)

Retention of internal data in the power-off
SEL succeeded in lowering the power consumption of
32-bit processors, ARM Cortex®-M0
(Reported with ARM and NOKIA at COOL Chips 2014)

NoffCPU can be efficiently driven in a normally-off manner utilizing the extremely low off-state current of the OSFET. For our report of the 8-bit CPU [4] in 2012, we have won an SSDM Best Paper Award [5]. In 2014, we prototyped a 32-bit CPU. The NoffCPU uses a nonvolatile flip-flop (FF) for the register in the CPU and a non-volatile memory for a memory. It has features of instant on/off operation and no power consumption in standby.

32bit CPU

Aiming for a "Sensor Network." CPU with "zero" standby power consumption
The increase of standby power due to miniaturization is a problem for silicon LSI. However, with normally-off driving using OSFET, the power consumption of the CPU and memory can be drastically decreased under the driving conditions of Case 2 and Case 3 for the sensor networks.


Case 1: active 1ms, sleep 1ms
Case 2: active 1ms, sleep 1s
Case 3: active 1ms, sleep 100s
1) Normally-off driving: Normally-off driving is a technology to reduce the power consumption of a CPU by turning off the power while in standby. In a typical CPU, the data is lost when it is turned off. Therefore, data transfer is needed every time the power is turned off for normally-off driving, leading to hindrance of power reduction. However, a CPU using OSFET can hold the internal state even when the power is shut off, resulting in a low-power-consumption CPU that enables efficient on/off operation and requires no power while being in standby.


[4] T. Ohmaru et al., “Eight-bit CPU with Nonvolatile Registers Capable of Holding Data for 40 Days at 85℃ Using Crystalline In-Ga-Zn Oxide Thin Film Transistors”, Ext. Abstr. Solid State Dev. Mater., 1144 (2012).
[5] SSDM Paper Award
http://www.sel.co.jp/news/news/2013-09_ssdm.html
[6] Reported with ARM and NOKIA. H. Tamura et al., “Embedded SRAM and Cortex-M0 core using a 60-nm crystalline oxide semiconductor”, IEEE Micro, 34, 42 (2014).



Image Sensor

Image sensor with global shutter technology2)

This is an image sensor created by utilizing OSFET's off-state characteristics. With this technology, an object moving at ultra-high speed can be captured without blurring[7].


Image Sensor

2) Global shutter technology is an ideal image sensor driving method by which the entire screen is captured at once, as opposed to the rolling shutter method used in devices such as digital cameras where an image is captured per scan line.

[7] T. Aoki et al., “Electronic Global Shutter CMOS Image Sensor using oxide semiconductor FET with Extremely Low Off-state Current”, IEEE Symp. VLSI Circuits Dig. Tech. Pap., 174 (2011).


* OSFET, DOSRAM, NOSRAM, and NoffCPU are registered trademarks of Semiconductor Energy Laboratory Co., Ltd. (Japanese trademark registration No. 5519759, No. 5519752, No. 5529056, and No. 5519756). Cortex is a registered trademark of ARM Ltd.