Yuichiro Ito

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

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.

Resolution improvement for HgCdTe IRCCD

This paper describes a resolution improvement for a mercury cadmium telluride (MCT) infrared charge-coupled device (IRCCD) using a new microscanner. To keep the microscanner compact, the scanner prism is placed between the lens and the IRCCD, and driven by a bimorph piezoelectric actuator. By compensating the drive pulse and optimizing the prism thickness, the microscanner gives a fast and stable response with low distortion. The medium wavelength imager developed for the microscanner gives a 128 X 128 pixel thermal image in the 3 to 5 micrometers band using a 64 X 64 element IRCCD. The Nyquist frequency was increased from 10 to 20 cycles/mm to reduce aliasing without decreasing the S/N ratio. The noise equivalent temperature difference (NETD) was measured at 0.06 K with an f-1.7 lens. The modulation transfer function (MTF) was estimated by considering the scan distortion and the pixel aperture profile. By optimizing the aperture profile of the photodiode, the MTF at the Nyquist frequency was increased from 0 to 20%.

A Two-Dimensional HgCdTe IRCCD with Increased Cell Capacity

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

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.

A Meander Channel CCD Infrared Imager With A Platinum Silicide Schottky Barrier

This paper describes a new configuration for a Schottky barrier IRCCD (SB-IRCCD). This device utilizes a Meander Channel CCD (MCCD) for both the vertical and horizontal readout registers. The MCCD has simple electrode configuration consisting of two straight gate electrodes over the meander channel without bus lines and contact holes. This simple electrode configuration increases the fill factor of SB-IRCCD and results in the improvement of its photoresponse. In addition, the versatile electrode configuration of the MCCD simplifies connection (in corner turns) between the vertical and horizontal readout registers. A 64 x 64-element monolithic Schottky barrier infrared meander channel CCD (SB-IRMCCD) with a 23 % fill factor was fabricated with a relaxed 10 μm design rule. This paper also discuss how a fill factor of 57 % will be possible by decreasing the area of the vertical MCCD register to 30 % of the present device.