Infrared(IR)photo detectors based on InAs/GaSb type II superlattice have developed quickly in recent years. Many groups show great interest in InAs/GaSb superlattice detector for its superiors as high quantum efficient, high working temperature, high uniformity and low dark current densities. Inductively coupled plasma(ICP) etching of GaSb and InAs/ GaSb superlattices were performed using Cl2/Ar/CH4/H2. This paper introduceste inductively coupled plasma( ICP) etching of Inas/GaSb with SiO2 mask by the Cl2/Ar/CH4/H2 mixed-gas process. The effects of process parameters such as gas combination, ICP and RF power on the etch rate and quality of InAs/GaSb It is found that the ratio of Cl2 flow rate significantly affects the etch rate, due to the trade-off between physical and chemical component of etching. The etch rate of InAs/GaSb increases with the increase of percent of Cl2, there will InClx remains in the etching channel when the etching depth exceeded 2μm, which can stop the etching going on. This phenomenon can be eliminated by decrease the Cl2 ratio,to make sure the etching depth reach 6μm under a certain low etching rate. The surface morphology and SEM of the superlattice material after etching shows that dry etching morphology is better than wet etching.After the electrode is grown, the superlattice chip have a good diode characteristic curve.
Small scale Readout Integrated Circuit (ROIC) still remain application requirements because of its lower cost, lower power and smaller structure size. A 128×128 format flexible small pixel ROIC was promoted in this paper. In the 30μm pitch pixel, an integration capacitance high to 2.1pF was realized, so the input charge handling ability can reach to 47 Million electrons. The ROIC can work in both integrate-then-read (ITR) and integrate-while-read (IWR) mode, which is decided by the integration signal. A serial data is used to realize some flexible functions, such as fixed windows select, output number select, anti-blooming and the detector bias voltage adjust. A 64×64 fixed window is selectable combined with the complete 128×128 array. Single output or two outputs can be selected for higher frame rate. By the means of the built-in digital to analog converter (DAC) circuits, the detector bias voltage can be changed from -600mV to 100mV. Some digital control methods are promoted to reduce the power consumption of the whole ROIC.
The defective elements from indium bump preparation in FPA fabrication are tested by optical microscopy and FPA testing bench. Results show that the defective elements from indium bump fabrication include connecting defective elements and missing defective elements. It is easy to identify missing defective elements by FPA testing bench because the response voltage of defective elements is zero and response voltage of other elements around defective element is higher than that of normal elements. And it is difficult to identify connecting defective elements by FPA testing bench because the response voltage of connecting defective elements is basically the same as that of normal elements. The defective elements from indium bump fabrication are due to the indium bump with connecting or missing caused by the process of photolithography, eroding and lift-off. Fabrication process such as photolithography, eroding and lift-off is optimized to reduce defective elements from indium bump fabrication.
For counteracting background current of photoconductive (PC) PbS detector, an example of layout design and analyze 1×128 linear PbS infrared focal plane array (IRFPA) detector using resistance selection of blind sensitive element is given. 1×128 linear PC PbS infrared focal plane array detector is fabricated and characterized by IRFPA test-bench. Results show that average responsivity of detector is 4.19×106V/W; average detectivity of detector is 5.79×109cm•Hz1/2•W-1.
Performance of IRFPA depends greatly on the amount and distribution of bad pixels. In this paper, general causes of bad
pixel in IRFPA are analyzed. Most bad pixels of IRFPA can be classified into four types for flip-chip bonding structure.
The amount of bad pixels in IRFPA often increases after long-term operation. This strongly affects application of IRFPA.
High temperature storage and temperature shock are effective ways to expose these potential bad pixels in advance. High
temperature storage and temperature shock are carried out on some IRFPA samples. Four kinds of variation for bad
pixels are investigated. They are variations of amount, characteristics, bad pixels on margin and bad pixels in different
IRFPA. Results show potential bad pixels damaged after these tests. New bad pixels are tested, analyzed and classified.
Each type of bad pixel is corresponding to defect of specified manufacture procedure. This indicates the potential
improving directions. Methods that could reduce bad pixels are briefly discussed. Results shown in this paper can help to
improve manufacture technology of IRFPA and then the performance of infrared imaging system.