Vladimir P. Reva

Sub-THz radiation room temperature sensitivity of long-channel silicon field effect transistors

Room temperature operating n-MOSFETs (n-type metal-oxide silicon field effect transistors) used for registration of sub-THz (sub-terahertz) radiation in the frequency range ν = 53−145 GHz are considered. n-MOSFETs were manufactured by 1-μm Si CMOS technology applied to epitaxial Si-layers (d ≈15 μm) deposited on thick Si substrates (d = 640 μm). It was shown that for transistors with the channel width to length ratio W/L = 20/3 μm without any special antennas used for radiation input, the noise equivalent power (NEP) for radiation frequency ν ≈76 GHz can reach NEP ∼6×10−10 W/Hz1/2. With estimated frequency dependent antenna effective area Sest for contact wires considered as antennas, the estimated possible noise equivalent power NEPpos for n-MOSFET structures themselves can be from ∼15 to ∼103 times better in the specral range of ν ∼55–78 GHz reaching NEPpos ≈10−12 W/Hz1/2.

Properties of 2x64 linear HgCdTe MBE-grown LWIR arrays with CCD silicon readouts

Mercury-Cadmium-Telluride (MCT) 2 X 64 linear arrays with silicon readouts were designed, manufactured and tested. NCT layers were grown by MBE method on (103) GaAs substrates with CdZnTe buffer layers. 50 X 50 mm n-p-type photodiodes were formed by 80 divided by 120 keV boron implantation. The dark current at 100 mV reversed biased diodes was within 15*30 nA and zero bias resistance-area product was within R0 approximately equals 20 divided by 50 Ohm X cm2. Silicon read-out circuits were designed, manufactured and tested. Read-outs with skimming and partitioning functions were manufactured by n-channel MOS technology with buried or surface channel CCD register. The parameters of LWIR MCT linear arrays with cutoff wavelength (lambda) co 10.0 divided by 12.2 micrometers and Si readouts were tested separately before hybridization. The HgCdTe arrays and Si readouts were hybridized by cold welding In bumps technology. With skimming mode used for integration time of 24-30 ms for such MCT n-p-junctions, the detectivity D*(lambda ) approximately equals 4 X 1010 cmXHz1/2/W. Dark carrier transport mechanisms in these diodes were calculated and compared with experimental data. Two major current mechanisms were included into the current balance equations: trap-assisted tunneling and Shockley-Reed-Hall generation-recombination processes via a defect trap level in the gap. Other current mechanisms (band-to-band tunneling, bulk diffusion) were taken into account as additive contributions. Tunneling rate characteristics were calculated within k-p approximation with the constant barrier electric field. Relatively good agreement with experimental data for diodes with large zero resistance-area products (R0A > 10 OhmXcm2) was obtained.

Readout device processing electronics for IR linear and focal plane arrays

Silicon read-out devices with input direct injection and buffered direct injection circuits and charge coupled devices (CCD) multiplexers to be used with n+-p- or p+-n-photovoltaic (PV) multielement arrays were designed, manufactured and tested in T equals 77-300 K temperature temperature region. Into these read-out devices were incorporated the testing switches which attach the sources of direct injection transistors to the common load resistors to imitate the output signal of mercury cadmium telluride photodiodes. The silicon read-out devices for 2 X 64 n+-p- or p(superscript +n- linear arrays and n(superscript +-p-2 X 4 X 128 time delay and integration arrays with skimming and partitioning functions were manufactured by n- or p-channel MOS technology with buried channel CCD register. The designed CCD readout devices are driven with four- or two-phase clock pulses.

Testing of readout device processing electronics for IR linear and focal plane arrays

For preliminary selection of the silicon read-out devices designed for applications in hybrid mercury-cadmium-telluride (MCT) IR linear or matrix arrays manufactured according to flip-chip technology, there was designed constructions of the testing circuits imbedded into the read-out devices to test them before hybridization. Also the procedure of their testing at room temperature without attachment to the MCT photo- voltaic multielement arrays was developed. There were designed some types of multielement silicon read-out devices with input direct injection and buffered direct injection circuits and charge coupled devices (CCD) multiplexers to be used with n+-p- or p+-n-photodiodes with dynamical resistance at reverse bias R greater than or equal to 107 (Omega) . Into these read-out devices there were incorporated the testing switches which attach the sources of direct injection transistors to the common load resistors to imitate the output signal of MCT photodiodes. The silicon read-out devices for 2 X 64 linear arrays and 2 X 4 X 128 (144) TDI arrays with direct and buffered direct charge injection were manufactured by n-channel MOS technology with CCD register with buried channel. By changing the frequency of the control impulses here were investigated the characteristics of the read-out devices for time delay and integration (TDI) arrays in the regime of integration and without it (in TDI channel).

576x6 ROIC for MCT LWIR arrays

Silicon ROIC for MCT LWIR 576x6 diode matrix arrays was designed. It includes 4 blocks of 144x6 arrays with 56x43 micron pixels. Diodes shift perpendicular to scanning direction is 0.25 of pixel size. ROICs were designed for their manufacturing by 0.6 micron design rules CMOS technology with 2 polysilicon levels and 2 metal levels. Six elements TDI function is used with bidirectional scanning, “dead” elements deselection, gain trim control, image data format and integration time selection, 8 levels input capacity programming, direct testing of the PV sensitive elements, etc. Max input capacity is 2.7 pC, the capacity at the TDI output register is about 2.0 pC, the output signal amplitude is not less than 2.8 V, the dynamic range is 77 dB. There are 8 video outputs, and the frequency range is 5 MHz.

Comparative analysis of 4x288 readouts and FPAs

Comparative analysis of four 4x288 different designed readouts elaborated at the Institute of Microdevices and the Institute of Semiconductor Physics is presented. Also some features of design 576x6 readouts adduced. All the readouts have the direct injection input circuit with incorporated cells allowing testing without photodiodes. TDI registers have three delay elements between neighbor inputs. Some characteristics of 4x288 FPAs with mercury-cadmium-telluride TDI arrays are cited too. 2-phase and 4-phase CCD readouts (2.5 micron technology) have different channel types (surface, buried and semi-buried), which include 10 bit TDI registers in each channel, and 18 channel multiplexing to 16 outputs. Two polysili-con, one metal level and 400 A dielectric layers were used. The readouts characteristics: charge handling capacity, transfer characteristics, output nonlinearity characteristics, bias dispersion, etc. are presented. CCD technology used for data multiplication results in crosstalk increase, because of the presence of rather considerable transfer inefficiency at cryogenic temperatures. Using 2.5 micron CCD technology and 2.0 CMOS technology the readouts, which include the digital interface for dead pixels deselection, preliminary amplification circuits, 36 channel multiplication by CCD registers and 2 beat multiplication by analogue switches to 4 output amplifiers, were manufactured. One pocket CMOS technology with two polysilicon, two metal levels and 350 A dielectric layers were used. To increase the linearity of transfer characteristics and noise level decrease at the output of CCD the circuits of charge-voltage conversion on the base of operational amplifiers were used. This allows getting circuits with parameters close to those obtained by 0.8 - 1.0 micron CMOS technology. Also some characteristics of 4x288 readouts designed by 1.2 micron CMOS technology are discussed (two polysilicon and two metal levels). This one includes the circuits of auxiliary electronics. Comparative analysis shows that the readouts mentioned are different in numbers of outputs, external service but have rather similar parameters.

MCT linear arrays and associated silicon readouts

MCT 2×64 and 4×288 linear arrays with silicon readouts were designed, manufactured and tested. (013) MCT MBE layers were grown on GaAs substrates with ZnTe and CdTe buffer layers. 2×64 arrays were also manufactured on the base of LPE layers on CdZnTe (111) substrates. 50×55 and ≈30×30 μm area n-p-type photodiodes were formed by 50 ÷ 120 keV boron implantation. The dark currents at V ≈ 100 mV reversed biased diodes used in arrays with cutoff wavelength λco ≈ 10.0 - 12.2 μm were within 15 - 50 nA and zero bias resistance-area products were within R0A ≈ 5 ÷ 20 Ohm×cm2. Designed silicon readouts with skimming and partitioning functions were manufactured by n-channel MOS technology with buried or surface channel CCD register. For achievement with the silicon readouts the deselection function, the “composite” technology approach was considered. In this case both the technology of n-channel CCD and CMOS technology were applied, which allow to weaken considerably the technological design rules for realization of 288×4 readouts with deselection of “dead” elements. It is shown that 2.5 μm design rules for CCD and 2.0 design rules for CMOS technologies allow to realize most of the functions needed for 288×4 MCT array operation with deselection function. Before hybridisation the parameters of MCT linear arrays and Si readouts were tested separately. HgCdTe arrays and Si readouts were hybridised by cold welding In bumps technology. In dependence of FOV with skimming mode used for integration time of 8 - 20 μs detectivities within D*λ (0.4 - 1.7)×1011 cm×Hz1/2/W were achieved in dependence of the array format. Dark carrier transport mechanisms in MCT diodes were calculated and compared with experimental data.

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.

Noise measurements of HgCdTe LWIR arrays with CCD readouts

Investigations of performance of mercury cadmium telluride (MCT) multipixel arrays at T≈80 K are considered. MCT hybrid arrays for long-wavelength infrared (LWIR) applications with n+-p-diodes and n-channel charged coupled devices (CCD) silicon readouts were designed, manufactured and tested. For testing procedure the measurements of noise and signal-to-noise ratio (SNR) are the key issues to determine performance parameters to characterize IR-sensors. That puts certain requirements to the registration system and methods of measuring used. The noise of the signals from LWIR-photodiodes with CCD readouts or CCD readouts itself was measured using several different techniques. To find out and eliminate noise sources the spectral noise power of signals was analyzed. It allowed the possibility to implement actions for reducing of the registration system noise, and to define the software noise filters to be used. The testing procedure of FPA performance characteristics includes the measurements of detectivity D*, noise equivalent temperature difference NETD, cut-off wavelength and some other parameters of the arrays.

Linear HgCdTe IR FPA 288×4 with bidirectional scanning

The long wavelength (8–12 μm) IR FPA 288×4 based on a hybrid assembly of n+-p diode photosensitive arrays (PA) of HgCdTe (MCT) MBE-grown structures and time delay integration (TDI) readout integrated circuits (ROIC) with bidirectional scanning have been developed, fabricated, and investigated. The p-type MCT structures were obtained by thermal annealing of as-grown n-type material in inert atmosphere. The MCT photosensitive layer with the composition 0.20–0.23 of mole fraction of CdTe was surrounded by the wide gap layers to decrease the recombination rate and surface leakage current. The diode arrays were fabricated by planar implantation of boron ions into p-MCT. The typical dark currents were about 4–7 nA at the reverse bias voltage of 150 mV. The differential resistance R was up to R0 = 1.6×107 Ω zero bias voltage, which corresponded to R0A ∼70 Ω ·cm2 and to the maximal value Rmax = 2.1 × 108 Ω. The bidirectional TDI deselecting ROIC was developed and fabricated by 1.0-μm CMOS technology with two metallic and two polysilicon layers.The IR FPAs were free of defect channels and have the average values of responsivity Sλ = 2.27×108 V/W, the detectivity Dλ* = 2.13 × 1011 cm × Hz1/2 × Wt1, and the noise equivalent temperature difference NETD = 9 mK.