A 640×480-17μm ROIC for uncooled microbolometer FPAs

Abstract

This paper reports the development of a new microbolometer Readout Integrated Circuit (ROIC), called MT6417BA. It has a format of 640 × 480 (VGA) and a pixel pitch of 17μm. MT6417BA is Mikro-Tasarim’s third microbolometer ROIC, which is developed specifically for surface micro-machined microbolometer detector arrays using high-TCR pixel materials, such as VO_x and a-Si. MT6417BA has a system-on-chip architecture, where all the timing, biasing, and pixel non-uniformity-correction (NUC) operations in the ROIC are applied using on-chip circuitry simplifying the use and system integration of this ROIC. MT6417BA has a serial programming interface that can be used to configure the programmable ROIC features and to load the NUC date to the ROIC. MT6417BA has a total of 4 analog video outputs and 2 analog reference outputs, placed at the top and bottom of the ROIC, which can be programmed to operate in the 1, 2, and 4-output modes and can support frames rates above 60 fps at 10 MHz pixel output rate. The ROIC is designed to support pixel resistance values ranging up to 100kΩ. MT6417BA is operated using conventional row based readout method, where pixels in the array are readout in a row-by-row basis, where they are biased and integrated using synchronously applied NUC data. The NUC data is applied continuously in a row-by-row basis using the serial programming interface operated at 20 MHz supporting frame rates as high as 60 fps. The bias voltage of the pixels can be programmed over a 1.0 V range to compensate for the changes in the detector resistance values due to the variations coming from the manufacturing process. The ROIC has an on-chip integrated temperature sensor with a sensitivity of better than 5 mV / K, and the output of the temperature sensor is embedded in the analog video stream. MT6417BA can be used to build a microbolometer FPAs with an NETD value below 50 mK using a microbolometer detector array fabrication technology with a nominal detector resistance of 60 KΩ, a high TCR value (> 3 % / K), and a sufficiently low pixel thermal conductance (G_th ≤ 10 nW / K). MT6417BA ROIC die measures 14.1 mm × 15.4 mm in a 180 nm CMOS. MT6417BA is fabricated on 200 mm diameter CMOS wafers with 100 parts per wafer. The microbolometer ROIC wafers are engineered to have flat surface finish to simplify the wafer level detector fabrication and wafer-level vacuum packaging (WLVP). The ROIC runs on 3.3 V analog and 1.8 V digital supplies, and dissipates less than 150 mW in the 2-output mode at 60 fps. Mikro-Tasarim provides tested ROIC wafers and offers compact test electronics and software for its ROIC customers to shorten their uncooled FPA and camera development cycles. Mikro-Tasarim has also recently developed a new programmable mixed-signal application specific integrated circuit (ASIC), called MTAS1410X4, which is designed to perform ROIC driving and digitization functions for microbolometer ROICs with analog outputs, such as MT6417BA and MT3825BA ROIC products of Mikro-Tasarim. MTAS1410X4 has 4 simultaneously working 14-bit analog-to-digital converters (ADCs) with integrated programmable gain amplifiers (PGAs), video input buffers, a programmable controller, and a flash memory interface for NUC operations. MT6417BA ROIC together with MTAS1410X4 ASIC can be used to develop low-noise and low-power uncooled microbolometer imaging sensors with compact camera electronics.