This paper reports the development of mid-wave 320x256 HgCdTe IRFPA with 30μm pixel pitch since 2002 in Korea.
All key technologies such as HgCdTe photodiode array fabrication process, the design of silicon readout integrated
circuit and hybridization process between HgCdTe photodiode array and ROIC including underfill encapsulation process
are studied and realized. The fabricated IRFPA shows good electro-optical performances such as operability over 99%,
NETD of ~ 17mK and there is no degradation in the operability during 500 thermal cycles.
CdTe films have been electrodeposited on HgCdTe from ethylene glycol based electrolyte containing 50 mM CdSO4, 10 mM K2TeO3 and 0.1 M HClO4. Deposition potential range with respect to a saturated calomel reference electrode was determined through cyclic voltammetry technique. RBS data showed that films deposited at potential range between -0.4 to -0.5 V have nearly stoichiometric Cd/Te atomic ratio. At the same time, highly oriented and smoother films were obtained at potential range were stoichiometric CdTe films were electrodeposited through nitrogen bubbling process. By adopting constant potential deposition technique could be obtained between electrodeposited CdTe and HgCdTe substrate showing high frequency capacitance-voltage (C-V) characteristics. Electrodeposited CdTe film can be used as a passivant for LWIR HgCdTe photodiodes.
Several junction formation methods are known to make HgCdTe photovoltaic devices. Ion implantation is the most popular process, but it needs additional thermal annealing process. In-situ junction formation by several epitaxy techniques is the advanced process, but is still hard to fabricate. In this paper, for the first time, hydrogenation technique for p-to-n type conversion in HgCdTe has been studied to fabricate HgCdTe photovoltaic infrared detector. H2 plasma generated in an inductively coupled plasma (ICP) system was used to hydrogenate p-type HgCdTe wafer. Using the ICP system, damages given to the HgCdTe wafer could be minimized. Junction depth measured by differential Hall measurement was able to be adjusted from 2μm to 20μm. Hydrogen atom profile was measured by secondary ion mass spectroscopy (SIMS) and doping profile was measured by differential Hall measurement. Similar depth profile was found between the hydrogen profile and doping profile. It suggests the diffused hydrogen atom is the source of the type conversion. Several experiments were also taken with vacancy-doped and gold-doped p-type HgCdTe wafers. Type conversion was observed only in vacancy doped HgCdTe wafer, not in gold-doped HgCdTe wafer. This means that junction formation by hydrogenation is not due to the damage by the hydrogen plasma, but due to the diffusion of the hydrogen atoms. By applying the hydrogenation process to vacancy-doped wafers, LWIR diodes were successfully fabricated. Current-voltage (I-V) characteristics of hydrogenated Hg0.79Cd0.21Te diodes were also measured. Average RoA products of these diodes were about 50 Ω cm2. Device uniformity and stability were also tested. The characteristics of the hydrogenated devices did not changed under the baking condition of 80°C over 10 days.
An experimental investigation was performed to study the heat transfer of flat micro heat pipe (FMHP) arrays with 38 triangular microgrooves. A heat pipe is an effective heat transport device that uses the latent heat of vaporization and operates without external power and achieves very high thermal conductance by means of two-phase fluid flow with capillary circulation. The overall size of the FMHP is 24 mm X 16 mm X 1.25 mm. The FMHP that can be put underneath microelectronic die and integrated into the electronic package of microelectronic device has been fabricated and characterized. Water was used as a working liquid. The fabrication and heat transfer details along with steady state horizontal orientation performance test results are presented. The experimental results show the temperature decrease of 12.1 degrees Celsius at the evaporator section for the input power of 5.9 W and the improvement of 28% in effective thermal conductivity.
In this paper, two different surface treatments for bulk HgCdTe are compared in the point of surface recombination velocity and diode dynamic resistance-voltage characteristics. One surface treatment, named as standard treatment, is only Br-MeOH etching and the other, named as nitric acid (HNO3) treatment, is composed of chemical oxidation with nitric acid after Br-MeOH etching and the removal of the oxide with ammonium hydroxide. After such surface treatments, gate- controlled diodes were fabricated and surface recombination velocity were measured to be 170 cm/s and 70 cm/s for the standard treatment and nitric acid treatment, respectively. And, the nitric acid treatment diode satisfied BLIP dynamic resistance characteristics regardless of the variation of the gate voltage. Moreover, from the measurement of capacitance- voltage characteristics, it was found that nitric acid treatment reduced the hysteresis width in the C-V curves of ZnS/HgCdTe MIS capacitor by one tenth compared to standard treatment. It is thought that the nitric acid treatment reduces surface-related defect and charge.
A new reflow method for indium bump of hybridized HgCdTe IRFPA is proposed using H2 plasma. Twenty micrometer height indium bump is easily achieved with this method. In the new method, H2 plasma makes the indium bump surface clean with removing the oxidized indium by H radical chemical reaction. Simultaneously, H2 plasma increases the temperature of indium bump above 160 degrees Celsius. This sphere shaped bump is easily deformed plastically with relatively small force. Force of 2 g/bump changes the 20 micrometer height bump to 10 micrometer. The flip-chip bonding technique using the new reflow method is characterized with shear strain strength measurement. It is found that bonding reliability can be improved owing to increased height and smooth surface.
Impact experiments have been performed to investigate the fracture phenomena in two different transparent targets: glass and PMMA. Early states after intense impulsive loading were observed by means of IMACON high speed camera and manganine pressure gage. The wave propagation and crack growth into targets were analyzed as a function of time. Microcracks are generated always behind the shock wave front. In glass, the release waves reflected from the free surfaces of target sides may cause to generate secondary cracks in front of the main fracture surface. The wave interaction due to different impedance on the target boundaries affects wave propagation and crack growth.