Toshiba Develops 1/4 Inch 330,000 Pixel Image Sensor Utilizing Common CMOS Process Technology

5 February, 1997

TOKYO -- Toshiba Corporation today announced a 330,000 pixel complementary metal oxide semiconductor (CMOS) 1/4-inch image sensor which offers a level of performance sufficient for use in digital still cameras. The prototype sensor was fabricated using the CMOS process, the most widely used semiconductor processing technology, and one which has the potential to realize significant structural and functional advantages over CCD image sensors, the standard imaging device for today's digital cameras.

The prototype CMOS sensor operates with single 5V power supply. It consumes only 30mW, approximately 1/10 of the power of a CCD.

The potential advantages of CMOS are attracting widespread industry attention as an alternative to CCDs in image sensors. In this emerging area, Toshiba's prototype image sensor represents a major breakthrough in achieving CMOS pixel cells small enough for application in commercial products.

Toshiba has optimized the pixel cell circuit structure to shrink its size and achieve new levels of integration. Each pixel cell, with such basic elements as photodiodes and transistors, is packed into 5.6 x 5.6 square microns, approximately 30% smaller than other CMOS pixel cells already announced. The new prototype sensor was fabricated using the 0.6 micron design rule CMOS technology. It is designed to support the 640 x480 pixel VGA format, and is suitable for application in products.

Advantages of CMOS Image Sensors
(1) Easy integration of the image sensor with other circuitry, including the control circuit for the sensor, memory, and other signal processing circuits. As the sensor is formed with the same process technology as other circuitry, it is better suited to development of a system-on-chip that will realize smaller cameras. CCDs operate at high voltages and assuring the isolation of each element used in the sensor requires a dedicated fabrication process much different from CMOS. It is difficult to integrate a CCD sensor with other circuits in a single chip system.

(2) CMOS sensors can be driven at a single, low level voltage, while CCD image sensors requires three separate levels of power supply, up to a maximum of 15V. The CMOS specification contributes to easier camera design and system integration.

(3) A low power consumption level, around 1/10 that of CCD.

A key issue in developing a practical CMOS image sensor is increasing the pixel integration level of the pixel. A high level of integration is essential to achieving high resolution images while retaining compact equipment. Until now, integration levels in CMOS image sensors has been limited by the large number of elements required for each individual pixel cell.

Recent progress in the digitization of information, communications and image sources is promoting increased combination of image data and other data sources. CMOS sensors are attracting attention, as the realization of commercial devices has the potential to contribute to the development of novel information and communications systems utilizing camera functions, as well as contributing to more compact, high performance digital cameras. Toshiba's new device achieves a breakthrough in the trade-off between high resolution images and compact camera size.

The CMOS sensor will be announced at the International Solid State Circuits Conference held from February 6 to 9 at San Francisco, California. The technology will be also presented at Tomorrow 21, an exhibition of Toshiba technologies, at Tokyo International Forum from March 4 to 9.

Major Specifications

Optical Format 1/4 inch
Effective Pixels 640 (H) x 480 (V) VGA Format
Pixel Size 5.6 x 5.6 square microns
Chip Size 6.4 x 5.4 square milimeter
Process 0.6 micron CMOS Double-Poly-Si/Double Metal
Saturation Level 700mV
Power Supply 5.0V
Power Dissipation 30mW

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