Toshio Kanno

Uncooled infrared focal plane array having 128 x 128 thermopile detector elements

A 128 X 128 element thermopile infrared image sensor has been developed. This device has a monolithically integrated structure to increase fill factor. The CCD for signal charge accumulation and signal charge read-out is fabricated on the silicon surface. Over the CCD, silicon dioxide diaphragms for thermal isolation are made by using micromachining technology. On each diaphragm, 32 pairs of p-type polysilicon and n-type polysilicon thermopile are formed. The noise equivalent temperature difference obtained by the device is 0.5 degree(s)C with an f/1 lens. Since the materials used are the same as those for silicon ICs, and since the whole fabrication process is carried out at the silicon IC plant, it can be said that a low cost uncooled infrared image sensor is realized by this technology.

Platinum Silicide Schottky-Barrier IR-CCD Image Sensors

A 64 × 32-element Si monolithic IR-CCD array with the improved PtSi/p-Si Schottky-Barrier (S.B.) detectors has been developed. The improvement of the photoyield was achieved by the structure with no interconnection metal over the detectors and the thinner PtSi film for the S.B. The physical mechanism of the higher photoyield is discussed taking into account the carrier reflection at interfaces (PtSi–Si and PtSi–SiN). The performance of the 64 × 32 IR-CCD was sufficient enough to obtain a thermal image in the 3 to 5 µm atmospheric window range.

Development of MBE-grown HgCdTe 64 x 64 FPA for long-wavelength IR detection

The HgCdTe (MCT) 64 X 64 focal plane array (FPA) for long wavelength infrared (LWIR) detection was developed, using MCT epilayers grown by molecular beam epitaxy (MBE). The n-on-p photodiode array has a cutoff wavelength of 10.7 micrometers . The readout circuit, with off focal plane integration capacitance, was designed for 77 K operation. These components were fabricated independently and were hybridized. The 97.8% operability was obtained. Photodiode characteristics for each pixel were measured directly. Mean R

256 X 256 Element Platinum Silicide Schottky-Barrier Infrared Charge-Coupled Device Image Sensor

o)A value of 1.9 (Omega) (DOT) cm2 and quantum efficiency of 0.3 were obtained. Using an infrared camera system with nonuniformity correction function, the infrared image was successfully demonstrated. An NETD (noise equivalent temperature difference) value of 0.117 K was attained with an F/2.5 optical lens under the 300 K background condition.

Development of LPE-grown HgCdTe 64 x 64 FPA with a cutoff wavelength of 10.6 μm

A 256 x 256 element PtSi Schottky-barrier 1R-CCD image sensor has been developed using a minimum design rule of 2 µm and a three-level polysilicon structure. The pixel size and chip size are 37 x 31 µm2 and 10 x 10 mm2, respectively. In spite of the small pixel size, a large fill factor of 25% has been obtained. The responsivity has been improved by use of a thin metal film and an optical cavity structure. The barrier height and quantum efficiency coefficient obtained from the array performance measurement are 0.23 eV and 0.15 eV -1, respectively. The noise equivalent temperature difference of about 0.1 K is obtained with f/1.4 optics and a 16.7 ms stare time. The noise in this case is limited by the shot noise of the detector. An infrared camera was also developed using the 256 x 256 element IR-CCD image sensor.

A Two-Dimensional HgCdTe IRCCD with Increased Cell Capacity

We have developed a hybrid HgCdTe focal plane array (FPA) for wavelengths from 8 to 11 micrometers . We describe how we fabricated our back illuminated 64 X 64-element photodiode array on a liquid phase epitaxial (LPE) HgCdTe wafer, and a Si CCD multiplexer with line address readout. We optimized carrier concentration in the p-type HgCdTe layer to maximize charge injection efficiency to the Si CCD readout circuit to more than 99.3%. We achieved excellent uniformity of characteristics of the photodiode array, which is very important for an IRFPA, by using LPE HgCdTe grown with a tipping method, and passivating the photodiode array with an anodic sulfide of HgCdTe. We obtained an average product of zero-bias resistance and area (RoA) of 9.1 (Omega) cm2 with a cutoff wavelength of 10.6 micrometers at 77 K. We used line address readout to give a large charge storage capacity of 4 X 107 electrons. We estimated a noise equivalent temperature difference (NETD) of 0.08 K with F/2.5 optics, including fixed pattern noise. We tried some preliminary experiments to reduce the crosstalk from photogenerated carriers which spread laterally into the epitaxial layer. We improved the modulation transfer function (MTF) at Nyquist spatial frequency from the conventional 35% to 60% by using a crosswise drain structure around each photosensitive n+ on p diode.

Evaluation Method For Infrared Focal Plane Arrays With Metal Insulator Semiconductor (MIS) Structure

A new chip organization for CCD multiplexers to increase the cell capacity is discussed. The chip uses the interlaced readout scheme, the MCCD and the storage/transfer common electrode configuration. These three techniques triple the conventional cell capacity. The CCD multiplexer is source-coupled with a 64 x 64 element HgCdTe photovoltaic array for 3-5 μm spectral region. The cell size of the CCD is 100 x 50 μm. The detector element pitch is 50 μm. The multiplexer has the charge handling capability of 1.1 x 107 electrons/cell. A 50 dB dynamic range is obtained for all 64 x 64 elements with 8% offset variation against 300 K background radiation and 14% responsivity variation. The mean detectivity D*λρ is 1.8 x 1011 cmHz1/2/W at peak wavelength of 4.7 μm. This IRCCD realizes wide dynamic range without sacrificing detectivity.

256 x 256 element HgCdTe hybrid IRFPA for 8- to 10-um band

This paper describes a new method of surface potential measurement for MIS infrared focal plane arrays. The key feature of this method is a charge sensitive amplifier which detects the surface potential directly. The surface potential is subject to photo-generated charge carriers stored in a potential well as well as the gate voltage. Therefore, this measurement can be used for both electronic and optical characterization of an MIS infrared imager such as an infrared charge coupled device (IRCCD) or an infrared charge injection device (IRCCD). Mercury cadmium telluride (HgCdTe) IRCIDs with 3 x 5 pixels were evaluated using this technique. The measurement was controlled by HP System 35 and proved more accurate, informative, and speedy than the conventional capacitance-voltage (C-V) measurement.

(c) The storage /transfer common electrode configuration increases the size of the

We developed a 256 by 256 element HgCdTe hybrid infrared focal plane array (IRFPA) for the 8 to 10 micrometer band. We used three technologies to develop this high-performance, long-wavelength, large-scale IRFPA. The first innovation was to glue a sapphire substrate to a thinned Si readout circuit to reduce the thermal expansion mismatch with a HgCdTe diode array fabricated on a CdZnTe substrate. The second was to fabricate an interlaced switched- FET readout circuit using a 3 micrometer CMOS process. This readout circuit has a storage capacity of more than 107 electrons and two video outputs capable of a 3.5 MHz data rate. The third was a HgCdTe diode array with an anodic sulfide passivation film and an optimized cutoff wavelength to reduce dark current and achieve high sensitivity. The noise equivalent temperature difference (NETD) was 0.06 K using f/2.5 optics. After 1000 thermal cycles (300 K - 80 K), there were no significant indium bump failures nor notable degradation in detector performance.