Lester J. Kozlowski

LWIR 128*128 GaAs/AlGaAs multiple quantum well hybrid focal plane array

The authors describe the fabrication and performance of a new type of hybrid focal plane array (FPA). The hybrid consists of a 128*128 GaAs/AlGaAs superlattice multiple-quantum-well detector array with peak response at 7.7 mu m mated to a high-performance CMOS readout with direct injection input. The quantum-well infrared photodetector (QWIP) array was fabricated by molecular-beam epitaxy (MBE). Optical gratings were excluded to facilitate evaluation of the basic detector-technology. The mean D* at 78 K was 5.76*10/sup 9/ cm- square root Hz/W. Total FPA 1/f noise was negligible, as corroborated by imagery having minimum resolvable temperature (MRT) of 30 mK at 0.07 cycles/mrad. No gain nonuniformity correction was used in the imaging demonstration. >

The HAWAII Infrared Detector Arrays: testing and astronomical characterization of prototype and science-grade devices

Abstract Two generations of prototypes of a HgCdTe infrared detector array with 1024 × 1024 pixels developed by the Rockwell International Science Center have been tested in the new Quick Infrared Camera (QUIRC) and an upgraded version of KSPEC a cross-dispersed near-infrared spectrograph, on the University of Hawaii 2.2 m telescope. The HAWAII (HgCdTe Astronomical Wide Area Infrared Imager) prototype devices achieved very good performance. The read-noise in correlated double sampling (CDS) is between 10 and 15 e − rms, depending on the conditions of the operations and the way read-noise is computed. The quantum efficiency in H and K is above 50%. The full-well capacity is above 10 5 e − at 0.5 V applied detector bias and is, in our system, limited by the dynamic range of the A/D converter. The residual excess dark-current problem known from NICMOS-3 devices (Hodapp et al., 1992) [PASP, 104, 441] is not fully resolved. However, it appears less serious in our first HAWAII prototype devices. Using KSPEC, operation under low background conditions has been tested. At an operating temperature of 65 K, and using up to 128 samples of multi-sampling, a read-noise of − and a dark current −1 /min has been demonstrated. Tests of fast sub-array reads for wavefront sensing were conducted using QUIRC. For a sub-array frame repeat time of 11 ms, a read-noise of 6 e − has been demonstrated. An engineering-grade second-generation HAWAII device with reliable hybridization is now in routine operation in KSPEC. The first science-grade HAWAII device has now been installed in the QUIRC camera and is in routine operation. Steven Beckwith

A novel simultaneous unipolar multispectral integrated technology approach for HgCdTe ir detectors and focal plane arrays

In the last few years Rockwell has developed a novel simultaneous unipolar multispectral integrated HgCdTe detector and focal plane array technology that is a natural and relatively straightforward derivative of our baseline double layer planar heterostructure (DLPH) molecular beam epitaxial (MBE) technology. Recently this technology was awarded a U.S. patent. This simultaneous unipolar multispectral integrated technology (SUMIT) shares the high performance characteristics of its DLPH antecedent. Two color focal plane arrays with low-1013 cm−2s−1 background limited detectivity performance (BLIP D*) have been obtained for mid-wave infrared (MWIR, 3–5 m) devices at T>130 K and for long-wave infrared (LWIR, 8–10 m) devices at T∼80 K.

Uniform low defect density molecular beam epitaxial HgCdTe

This paper describes recent advances in MBE HgCdTe technology. A new 3 inch production molecular beam epitaxy (MBE) system, Riber Model 32P, was installed at Rockwell in 1994. The growth technology developed over the years at Rockwell using the Riber 2300 R&D system was transferred to the 32P system in less than six months. This short period of technology transfer attests to our understanding of the MBE HgCdTe growth dynamics and the key growth parameters. Device quality material is being grown routinely in this new system. Further advances have been made to achieve better growth control. One of the biggest challenges in the growth of MBE HgCdTe is the day-to-day control of the substrate surface temperature at nucleation and during growth. This paper describes techniques that have led to growth temperature reproducibility within + - 1°C, and a variation in temperature during substrate rotation within 0.5°C. The rotation of the substrate during growth has improved the uniformity of the grown layers. The measured uniformity data on composition for a typical 3 cm × 3 cm MBE HgCdTe/CdZnTe shows the average and standard deviation values of 0.229 and 0.0006, respectively. Similarly, the average and standard deviation for the layer thickness are 7.5 and 0.06 µm, respectively. P-on-n LWIR test structure photodiodes fabricated using material grown by the new system and using rotation during growth have resulted in high-performance (R0)A, quantum efficiency) devices at 77 and 40K. In addition, 128 × 28 focal plane arrays with excellent performance and operability have been demonstrated.

256*256 hybrid HgCdTe infrared focal plane arrays

Hybrid HgCdTe 256*256 focal plane arrays have been developed to meet the sensitivity, resolution, and field-of-view requirements of high-performance medium-wavelength infrared (MWIR) imaging systems. The detector arrays for these hybrids are fabricated on substrates that reduce or eliminate the thermal expansion mismatch to the silicon readout circuit. The readouts are foundry-processed CMOS switched-FET circuits that have charge capacities greater than 10/sup 7/ electrons and a single video output capable of 20-MHz data rates. The high quantum efficiency, tunable absorption wavelength, and broad operating temperature range of these large HgCdTe staring focal plane arrays give them significant advantages over competing sensors. The mature Producible Alternative to CdTe for Epitaxy-1 (PACE-1) technology, using sapphire detector substrates, has demonstrated 256*256 MWIR arrays with mean laboratory noise equivalent temperature difference (NETD) of 9 mK for a 4.9- mu m cutoff wavelength, 40- mu m pixel size, and 80-K operating temperature. RMS detector response nonuniformities are less than 4%, and pixel yields are greater than 99%. The newly developed PACE-3 process uses silicon for the detector substrate to eliminate completely the thermal mismatch with the silicon readout circuit. It has the potential for similar performance in even larger array sizes. A 640*480 hybrid array is under development. >

HAWAII-2RG: a 2k x 2k CMOS multiplexer for low and high background astronomy applications

The HAWAII-2RG is a major upgrade of our prior 2048 x 2048 CMOS readout for astronomy (HAWAII-2) to support the requirements of the Next Generation Space Telescope and enable breakthrough capability for ground-based astronomy. By migrating to 0.25μm CMOS, for the first time guide mode readout is simultaneously supported in combination with various programmable science modes on a frame-by-frame basis. Consequently, the readout simultaneously supports programmable guide mode window and full-field science using the rest of the 4.2 million pixels at read noise <5 e-. Also for the first time with any imaging sensor, low and high background astronomy is supported using from 1 to 32 low-noise outputs via low-speed and high-speed signal paths. The latter supports throughput rate of up 320 MHz for real time imaging at >60 Hz. As with the HAWAII-2, the readout can be mated to our infrared and visible detector arrays including low dark current MBE HgCdTe at cutoff wavelengths from 1.5μm to 14μm, 2.5μm PACE HgCdTe, and silicon p-i-n detectors with superior quantum efficiency to backside-illuminated CCDs.

Performance limits in visible and infrared imager sensors

Emerging CMOS image sensors are fundamentally superior to CCD imagers with respect to read noise and sensitivity at video data rates. We discuss each technologys performance limits, show that CMOSs advantages increase with the number of pixels, report supporting data and conclude that CMOS will likely supplant CCDs for megapixel imagers. CCDs can perform at their theoretical limit with minimum read noise of /spl sim/1 e- at 20 kHz data rate and 10-20 e- at /spl sim/10 MHz. CMOS-based image sensors, on the other hand, can provide higher sensitivity and lower read noise at /spl ges/10 MHz via pixel-based amplification and narrow noise bandwidth.

Pixel noise suppression via SoC management of tapered reset in a 1920/spl times/1080 CMOS image sensor

Correlated double sampling is widely used in imaging arrays to eliminate noise generated when a CCDs sense capacitance or a CMOS sensors photodiode is reset after signal integration and readout. Instead, we suppress photodiode kTC noise using a SoC implementation for progressive reset; supporting SoC components include a feedback amplifier having elements distributed amongst the pixel and column buffer, a tapered reset clock waveform, and reset timing generator. The reset method does not swell pixel area, compel processing of the correlated reset and signal values, or require additional memory. Theoretical analysis is presented along with experimental results. Integrated in a 1920 by 1080 imager having 5 /spl mu/m by 5 /spl mu/m pixels in 0.25-/spl mu/m CMOS, measured random noise for 5.5-fF detector capacitance is /spl sim/8 e- to 225 MHz video rate with image lag <0.12%. Random noise of /spl sim/30 e- is otherwise predicted and achieved using conventional reset. Sensor S/N ratio with progressive readout is /spl ges/52 dB at 60 Hz and 72 Hz frame rate.

Performance of HgCdTe, InGaAs and quantum well GaAs/AlGaAs staring infrared focal plane arrays

The ability to hybridize various detector arrays in disparate technologies to an assortment of state-of-the-art silicon readouts has enabled direct comparison of key IR detector technologies including photovoltaic (PV) HgCdTe/Al2O3, PV HgCdTe/CdZnTe, PV InGaAs/InP, and the photoconductive (PC) GaAs/AlGaAs quantum well IR photodetector (QWIP). The staring focal plane arrays range in size from 64 X 64 to 1024 X 1024; we compare these IR detector technologies versus operating temperature and background flux via hybrid FPA test at operating temperatures from 32.5 K to room temperature and photon backgrounds from mid-105 to approximately equals 1017 photons/cm2-s. Several state-of-the-art IR FPAs are included: a 1.7 micrometers 128 X 128 InGaAs hybrid FPA with room temperature D of 1.5 X 1013 cm-Hz1/2/W and 195K D of 1.1 X 1015 cm-Hz1/2/W; a 3.2 micrometers 1024 X 1024 FPA for surveillance; a 4.6 micrometers 256 X 256 HgCdTe/Al2O3 FPA for imaging with BLIP NE(Delta) T of 2.8 mK at 95K; and a 9 micrometers 128 X 128 GaAs QWIP with 32.5 K D > 1014 cm-Hz1/2/W at 32.5K and 8 X 1010 cm-Hz1/2W at 62K.

Theoretical basis and experimental confirmation: why a CMOS imager is superior to a CCD

Sub-micron CMOS has already enabled the development of IR focal plane array with ultra-low read noise and high sensitivity for many demanding applications. The successful monolithic integration of silicon photo detector with low- noise pixel-based amplifiers in fine pixel pitch via modern CMOS technology now suggests the imminent obsolescence of CCDs and photographic film for consumer uses. Specifically, we report the achievement of < 20 e- read noise at high data rates and video frame rate,s the confirmation of the fundamental superiority of the CMOS imager for visible imaging, and approximately 2X reduction in kTC noise without invoking classical correlated double sampling techniques. These suggest a strong likelihood reduction in kTC noise without invoking classical correlated double sampling techniques. These suggest a strong likelihood that the CCDs long reign is coming to an end.