Anatoly G. Klimenko

Focal plane arrays based on HgCdTe epitaxial layers MBE-grown on GaAs substrates

Heterostructures HgCdTe/CdTe/GaAs grown by molecular beam epitaxy were used for LWIR FPA fabrication. The technology was developed and 32 by 32 and 128 by 128 photodiode arrays with indium bumps of 15 micrometer height in each pixel were fabricated. Mean NEP is 1.7 by 10-13 W/Hz1/2 and 1.1 by 10-14 W/Hz1/2 for 128 by 128 photodiode arrays with (lambda) c value of 10.4 micrometer and 5.2 micrometer correspondently. The technology of hybrid assembling with continuous control of cold welding on the measuring stand was demonstrated on the example of 32 by 32 LWIR FPA. Mean NEP value of 5.4 by 10-14 W/Hz1/2 with (lambda) c equals 10.6 micrometer at 80 K operation were obtained. using an infrared camera system the infrared image was successfully demonstrated. The NETD value of 0.077 K was obtained under 293 K background condition.

The 4×288 linear FPA on the heteroepitaxial Hg 1-x Cd x Te base

x4×288 heteroepitaxial mercury-cadmium telluride (MCT) linear arrays for long wavelength infrared (LWIR) applications with 28×25 micron diodes and charge coupled devices (CCD) silicon readouts were designed, manufactured and tested. MCT heteroepitaxial layers were grown by MBE technology on (013) GaAs substrates with CdZnTe buffer layers and have cutoff wavelength λco ≈ 11.8 μm at T = 78 K. To decrease the surface influence of the carriers recombination processes the layers with composition changes and its increase both toward the surface and HgCdTe/CdZnTe boundary were grown. Silicon read-outs with CCD multiplexers with input direct injection circuits were designed, manufactured and tested. The testing procedure to qualify read-out integrated circuits (ROICs) on wafer level at T = 300 K was worked out. The silicon read-outs for 4×288 arrays, with skimming and partitioning functions included were manufactured by n-channel MOS technology with buried or surface channel CCD register. Designed CCD readouts are driven with four- or two-phase clock pulses. The HgCdTe arrays and Si CCD readouts were hybridized by cold welding indium bumps technology. With skimming mode used for 4×288 MCT n-p-junctions, the detectivity was about (formula available in paper) for background temperature Tb = 295 K.

Influence of dislocation on the performance of MBE Cd0,22Hg0,78Te photodiodes

The investigation of MBE CdHgTe photodiode characteristics after pressure applying to n-type of junction has been carried out. The diodes parameters have been studied in the temperature range of 5 divided by 120 K. It was found that the mechanical stress causes the increase of traps amount with Et approximately equals Ev plus 0.043 eV and Et approximately equals Ev plus 0.032 eV. The energies of these traps have some temperature dependence. The diodes generation-recombination and trap-assisted tunneling currents significantly increase at forward and reverse biases. The value of RoA decreases in an order at T less than 60 K because of trap assisted tunneling via the dislocation levels. At high temperatures T greater than 60 K the value of RoA does not change and determined by the diffusion mechanism.

Image conversion in uncooled mosaic microbolometer detectors for the IR and terahertz regions with a format up to 3072 × 576 or more

This paper discusses the process-design principles for creating hyperlarge-format mosaic photodetectors (MPDs), based on the butt-joining process of silicon chips with uncooled small-format microbolometer detector arrays (MBDAs). The basic unit is investigated and optimized for the process operations of laser scribing as part of the high-precision butt-joining process of chips in which the process part of the blind zone between the photosensitive edge elements of adjacent MBDA chips has a total size no greater than 30 μm. The design and layout are synthesized for 384×288-format silicon multiplexers, from which a 3072×576-format MPD fabricated using the butt-joining process developed here can provide better than 99% image-conversion efficiency for IR microbolometers and up to 100% for terahertz-range microbolometers.

A technology for assembling large-format infrared photodetector modules on indium microposts

The initial plane-parallel position of a photodetector array (PDA) and a silicon multiplexer (MUX) is brought about when the tops of the indium microposts are in contact under the action of only the force of gravity on the PDA. We orient the crystals (along xy) in visible light, and we use offset reference marks on the PDAs. We bring chains of laser microholes in the polyimide of the offset reference marks into coincidence with the reference marks on the MUX. We take into account the initial errors of all the axial lines; the alignment error reaches +/-0.4μm (along xy). At all stages of the assembly, the MUX is connected, and we observe the touching and the welding of the microposts. To avoid warping the planar transistors (along z), we use stops of suitable height, placed along the perimeter of the PDA.

Thermal Conductivity Measurements of Si-SiO2-Si Sandwich Structures for Micro/Nano Electronics

There are many applications that use SiO2 in microelectronics systems for electrical and thermal isolation. A recent nano-electronic development necessitated understanding of the thermal performance of Si-SiO2 -Si sandwich structures so that system level performance can be achieved. Based on a literature search, there have been numerous papers on Si-SiO2 structures, but none that dealt with a complete sandwich. Therefore our research designed, built and tested these sandwich devices to understand the thermal conductivity of the bonding layer. In this paper the transverse thermal conductivity through a Si-SiO2 -Si sandwich, where the two layers of Silicon are heavily doped, is measured and used to calculate the thermal conductivity through the thin oxide film. Test samples have been manufactured in a class-1000 clean room with Silicon microfabrication techniques to deposit the thin films. Control of the interfaces depends on the chermical bond due to thin film deposition, so no additional thermal interface materials were used in the actual samples. While in the literature various techniques such as thermal reflectance, 3-Omega, and micro thermocouples have been widely used to determine the thermal conductivity of thin oxide films, in this study we explored two techniques based on a transient and a steady state measurement. First, a laser flash technique was utilized to measure the thermal diffusivity to obtain the thermal conductivity. A MicroFlash meter equipped with a custom-made holder was employed. Four different thickness square samples (5×5 mm) with oxide thicknesses of 56, 210, 1011 and 2136 nm were tested. Second, the same samples were tested via steady state measurements employing micro thermocouples. Results show that thin film oxide thermal conductivity follows the bulk oxide thermal conductivity, published as 1.4 W/m-K at room temperature, but then falls as oxide thickness decreases. A further study has been performed to better understand the uncertainty in the experimental measurements. It is found that uncertainty in the oxide thermal conductivity is on average 122%, 78%, 21% and 19% (higher uncertainties for the lower oxide thicknesses) within 95% confidence level for laser flash measurements. The effect of noise parameters such as settling time, nitrogen level and sample preparation have also been studied during the laser flash measurements.Copyright

Mid- and Long-Wave IR Detectors Using an Hg1 – xCdxTe Heteroepitaxial Layer

A complete production technology is developed for single-cell and array IR detectors using an MBE-grown Hg1 – x CdxTe heteroepitaxial layer. The array detectors implement a bump-bonded flip-chip hybrid architecture. The arrays are constructed in photodiodes and have a size of 128 × 128 or 4 × 288. The single-cell detectors are built around a photoconductivity cell. The detectors are operated in the wavelength range 3–5 or 8–12 μm and at 78–80 or 200–220 K. Some performance data on the detectors are presented.

2X64 linear LWIR arrays based in HgCdTe MBE-grown layers and CCD silicon readouts

Two X sixty-four linear photodiode arrays on the base of HgCdTe MBE grown layers with CCD silicon readouts were designed, fabricated and tested. It is shown that detectivity for the given arrays even with skimming mode used for long integration times that is need for large square n-p-junctions used and cut-off wavelength of 12.2 micrometer was near the ultimate performance limit.

128 X 128 IR FPA based on GaAs/AlGaAs MQW

In this paper the experimental results on designing of 128X128 FPA for far IR spectrum range are presented. The module is a hybrid assembly of the photodetectors array based on GaAs/AlGaAs multiquantum wells and silicon multiplexer. The noise equivalent difference of temperature of the photodetector module NEDT=0.067 K at T=65 K.

128x128 hybrid FPAs using MBE HgCdTe films on GaAs substrates

The technology was developed and 128 X 128 LWIR FPAs based on HgCdTe epitaxial layers MBE-grown on GaAs substrates with cutoff wavelength (lambda) c equals 8 micrometer and 13 micrometer was fabricated. The photosensing layer HgCdTe was graded-gap layer with the higher content of Cd to boundaries of a layer. The manufactured LWIR FPAs had NETD 32 mK and 17 mK for (lambda) c equals 8 micrometer and 13 micrometer, correspondingly, at 295 K background and 80 K operation temperatures.