A Readout Integrated Circuit (ROIC) for GaN ultraviolet (UV) focal plane array (FPA) working in “solar-blind” band is studied in this paper. It has a format of 320×256 and a pixel pitch of 30μm. This circuit can operate both in integrating-while-reading (IWR) and integrating-then-reading (ITR) mode with the frame rate higher than 100fps. It is common that trade-offs always exist between chip power consumption and performances in integrated circuits design. In order to get high injection efficiency with small area and low power, A novel low-power capacitive-feedback trans-impedance amplifier (CTIA) with snapshot mode is designed for the proposed circuit. The smallest operational current of CTIA is only 10nA for 5V power supply. The total power consumption of ROIC is reduced significantly to 45mW with the ultra-low-power pixel. By adopting the 0.35μm 2P4M mixed signal process, the high-performance CTIA architecture can make two gain selections which charge capacities are 3.4Me - and 0.16Me - per pixel with 2.5 V output range. According to the experimental results, this circuit works well under 5V power supply and achieves 8MHz pixel-data-transmission rate.
Corona discharges occur in high voltage electrical equipment in case of defects and damage, while ultraviolet(UV) light generated during discharge. High resolution imaging in the solar-blind UV bands has a lot of applications in corona discharge detection. A ultraviolet imager based on 320×256 solar-blind AlGaN focal plane arrays (FPA) was designed that work even in the sunlight, because the Cut-off wavelength of the AlGaN FPA is 280nm. The UV image signal processing system based on FPGA is composed of various function modules include the voltage bias, sequence drive, A/D data acquisition, non-uniformity correction, video transformation. Due to FPGA-based data acquisition and realtime image processing technology, the UV imager can operate at a rate up to 100 frame/s. The results show that the simulation high voltage ultraviolet image can be obtained by the UV imager. The image non-uniformity correction performed is one-points correction method to realize background subtraction. And the images show good uniformity and contrast. The UV image of the alcohol burner flame can be detected by the Ultraviolet Imager. Imaging quality was discussed which can be determined by signal-to-noise ratio (SNR), the integration time, the optics f/number and so on. The best imaging conditions were analyzed and the imaging system was designed and setup. The conclusion is proved that the ultraviolet imager based on solar-blind AlGaN FPA provides a new method for corona discharge detection of high voltage power transmission and distribution system.
Thermal stability of Atomic Layer Deposition Al2O3 film on HgCdTe was investigated by Al2O3 film post-deposition annealing treatment and Metal-Insulator-Semiconductor device low-temperature baking treatment. The effectiveness of Al2O3 film was evaluated by measuring the minority carrier lifetime and capacitance versus voltage characteristics. After annealing treatment, the minority carrier lifetime of the HgCdTe sample presented a slight decrease. Furthermore, the fixed charge density and the slow charge density decreased significantly in the annealed MIS device. After baking treatment, the fixed charge density and the slow charge density of the unannealed and annealed MIS devices decreased and increased, respectively.
Silicon nitride (SiNx) films on GaN were deposited, using the inductively coupled plasma chemical vapor deposition
(ICPCVD) method with different radio-frequency chuck power (RF power). After deposition, all the films were annealed
at 750℃ in N2, and some pins and bubbles were observed on the surface of some films, but this phenomenon was not
observed on the films which were deposited with RF power=0W, as well as films deposited by a two-step-deposition
method, which was consisted of setting RF power=0W at the beginning, and setting RF power=2W after that. To study
the mechanism of origin of these pins and bubbles, Atomic force microscopy(AFM) was performed to study surface
morphology and measure the height of the pins and bubbles, it was found that the height of bubbles was about 300nm,
and the depth of pins was about 300nm, which were almost the same as the film thickness. It was showed that the pins
and bubbles were originated from gas escaping from the inner films after high-temperature annealing. X-ray
photoelectron spectra(XPS) was used to characterize the chemical composition of the films before and after annealing,
independently. It was found that, on GaN-SiNx interface and SiNx film surface, the N element content decreased a lot
after annealing, but N content remained almost the same in those films with RF power=0W. which indicated that
reducing of N content was closely related with those pins and bubbles. RF power increased the plasma energy and caused
GaN surface damage. The ion bombardment broke some N-Si bonds and N-Ga bonds, as a result some N reactants didn’t
perform as Si-N bond, but performed in other bonds such as N-H bonds or N-N bonds, and a high-temperature annealing
process would cause NH3 or N2 escape from the film. The pins were voids which resulted from the film broken by the gas, and the bubbles came from bulge resulted from gas escape.
The fabrication and characterization of InGaN ultraviolet photodetector were reported in this work. The effects of thermal annealing were investigated on the properties of ohmic contact. Experiments showed that the zero bias resistance was lowest when the sample was annealed at 550 degrees Celsius for 5 minutes. The current-voltage (I-V) curve showed that current at zero bias was 3.70×10-13A and the resistance was 4.53×1010 Ω. A flat band spectral response was achieved in the 360nm~390nm. The detector displayed an unbiased response of 0.22A/W at 378 nm, corresponding to an internal quantum efficiency of 88%. R0A values up to 1.3×108Ω·cm2 was obtained corresponding to D*=1.97×1013cm•Hz1/2•W-1.
Proc. SPIE. 7658, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optoelectronic Materials and Devices for Detector, Imager, Display, and Energy Conversion Technology
KEYWORDS: Infrared detectors, Accelerated life testing, Infrared sensors, Sensors, Microscopy, Photoresistors, Reliability, Infrared radiation, Failure analysis, Temperature metrology
This paper concerns HgCdTe (MCT) infrared photoconductor detectors with high operating temperature. The near room
temperature operation of detectors have advantages of light weight, less cost and convenient usage. Their performances
are modest and they suffer from reliable problems. These detectors face with stability of the package, chip bonding area
and passivation layers. It's important to evaluate and improve the reliability of such detectors. Defective detectors were
studied with SEM(Scanning electron microscope) and microscopy. Statistically significant differences were observed
between the influence of operating temperature and the influence of humidity. It was also found that humility has
statistically significant influence upon the stability of the chip bonding and passivation layers, and the amount of
humility isn't strongly correlated to the damage on the surface. Considering about the commonly found failures modes in
detectors, special test structures were designed to improve the reliability of detectors. An accelerated life test was also
implemented to estimate the lifetime of the high operating temperature MCT photoconductor detectors.
Recently, high-Al-content AlGaN alloy systems have attracted increasing attention, and it is urgent and
important to achieve excellent Ohmic contacts with low specific contact resistivity, good thermally stability, clear
borderline and smooth surface morphology of this alloy systems to optimize the performance of photoelectric
devices. In the experiment, we found that surface disordered layer and oxides including native oxide could be
removed by boiling KOH solution. The surface status of both samples was evaluated with scanning electron
microscope (SEM) and X-ray photoelectron spectra (XPS). For comparison, then A Ti/Al/Ti/Au multilayer was
deposited on the samples with and without wet chemical etching to observe their electric properties. After annealing,
I-Vcharacteristics via Keyley236 electric analyzer was measured. Ohmic contacts with the contact specific resistivity
of 6.55×10-4Ωcm2 were obtained between treated samples and the multi-metals. However, nonlinear I-V curves
indicated that the contact on the untreated sample was still the Schottky contact.
We have investigated wet chemical etching process of n+-type Al0.33Ga0.67N in 20% (by weight) aqueous KOH solutions
at 106°C after Ar+ ion beam dry etching treatment. Scanning electron microscope and Auger electron spectroscopy were
employed to characterize the surface morphology and stoichiometry with and without wet chemical etching. It is obvious
that dry etching damages were reduced after wet chemical etching. We also fabricated two sets of visible-blind p-i-n
detectors for comparison. I-V characterization indicated that the average leakage current of the wet etching treated
detectors was lower than that of the detectors without treatment by about one order of magnitude. When the reverse bias
was -5 V, the leakage currents of wet etching treated devices varied from -2.16×10-9 to -6.26×10-9 A and those of
untreated detectors varied from -2.68×10-8 to -3.49×10-8 A. The peak responsivity at 365 nm was also tremendously
enhanced by means of wet chemical etching treatment. It was 0.10 and 0.03 A/W under back illumination, with and
without wet chemical treatment, respectively. When the detector was under front illumination, the result was 0.05 and
0.02 A/W, respectively.
In recent years, AlGaN semiconductor alloys, with a direct bandgap tunable between 3.4eV and 6.2eV, become the most
suitable material for fabricating UV detectors. In this paper, a backside-illuminated visible-blind UV detector based on a
GaN/AlGaN p-i-n heterostructure has been successfully fabricated and tested. The p-i-n photodiode structure consists of
a 0.7um n-type Al0.33Ga0.67N:Si layer grown by metal-organic chemical vapor deposition (MOCVD) onto a low
temperature AlN buffer layer on a polished sapphire substrate. On the top of this layer there is a 0.18um undoped GaN
active layer and a 0.15um p-type GaN:Mg top layer. Square mesas of area A=1.70×10-3cm2 were obtained by inductively coupled plasma etching using BCl3, Ar and Cl2. Standard photolithographic and metallization procedures were also employed to fabricate the devices. The visible blind photodiode exhibits a narrow UV spectral responsibility band
peaked at 360nm, with maximum responsibility R=0.21A/W, corresponding to an internal quantum efficiency of 82%.
R0A values up to 2.64×108Ω•cm2 were obtained, corresponding to D*=2.65×1013 cmHz1/2W-1 at 360nm. The leakage
current at zero bias is 5.20×10-13A. We also examined GaN/AlGaN epitaxial layers by high resolution X-ray diffraction (HRXRD). The rocking curve indicates the multiple layers including p-type layer are in good state, which indicates that
the crystalline quality of films is the key of device performances.
Four-band HgCdTe infrared (IR) detector is developed for the first operational Chinese geostationary meteorological satellite FY-2C launched on October 19, 2004. As the Visible Infrared Spin-Scan Radiometer (VISSR) is the primary payload on FY-2C, the IR detector is one of the most important modules for such an imaging instrument. Compared with its predecessors FY-2A and FY-2B (experimental models, launched in June 1997 and June 2000 respectively), the detector used in FY-2C is quite different in band selection and detector package. The four band IR detector for FY-2C application consists of four photoconductive (PC) detector chips made of Hg1-xCdxTe with different compositions x , corresponding to the wavelengths of 3.5 to 4.0μm, 6.3 to 7.6μm, 10.3 to 11.3μm and 11.5 to 12.5μm respectively. Four cooled IR filters are included in one detector package, which enables us to simplify the system without any IR beam splitters and IR filters outside the detector for defining separate bands. The IR detector operates at radiative cooler temperature ranging from 92 to 102K. This paper reviews the design, process and packaging for the four-band IR detector used in FY-2C satellite. The performances and related aspects of this detector are also presented.
In this paper, low frequency noise has been investigated in SWIR HgCdTe photodiodes from 4Hz to 3.2 KHz at different reverse bias. At low frequency the noise mainly consists of flicker noise and generation recombination (g-r) noise while at high frequency thermal noise is the dominant component. The flicker noise current is proportional to the detector current at small reverse bias, and the Hooge parameter αH of the device is evaluated. In addition, the low frequency noise at 100mV reverse bias measured from 250-300K are reported. The fluctuation time constant of g-r noise is extracted by fitting the curve of the low frequency noise, and the trap thermal activation energy of the deep level is obtained from the relation of τ and temperature.
The minor carrier effective lifetime of middle wavelength infrared HgCdTe photoconductive sensors is relatively large. The sweep-out effect may easily emerge in small size sensors which decrease the responsitivity. In order to eliminate this effect, an overlap structure is often used. In this paper the low frequency noise characteristics of HgCdTe sensors with this overlap structure is studied. It is shown that not only the low frequency noise of sensors with this overlap structure is much larger than that of the conventional ones, but also Hooge parameter and frequency exponent are changed with bias current especially for this overlap structure. An edge-contacted asymmetrical metal-insulator-semiconductor model is presented to explain the noise characterization. It is found that a depletion layer would appear from the HgCdTe surface under overlap electrodes when the sensors are biased. Its thickness changed with its position because of the difference of the voltage. When the bias current is increased, this depletion layer is widening. Also Hooge parameter and frequency exponent increased which are similar to the MISFETs. It is shown by experiments that the enhancement of sensor noise for overlap structure is mainly caused by the depletion layer under overlap electrodes.