Large format high resolution FPAs are the key elements for medium to high performance applications including enhanced vision, thermal sights, and industrial applications. In this work, the characteristics of recently developed 10 μm pitch SXGA InSb detector are presented. To develop the 10 μm pitch SXGA InSb detector, three important technical issues were resolved. At first, physically isolating pixels to reduce the crosstalk was adopted to enhance the Modulation Transfer Function (MTF). It was found that the MTF of fabricated detector tested with slanted edge method was improved largely. The MTF of 10 μm pitch FPAs at the Nyquist frequency showed the same MTF of 15 μm pitch device at the Nyquist frequency. Therefore the zoomed image of 10 μm pitch device will have the same image quality as the 15 μm device. Another important issue is the indium bump fabrication process. To fabricate fine bump with uniform height, electrodeposition technology was developed. With this method, uniform indium bump over the 8' ROIC could be achieved. Finally, to achieve large capacitance, 0.18 μm CMOS technology was adopted. To use 0.18 μm CMOS technology, the ROIC should have to be designed all again. The designed and fabricated ROIC has 2.4 Me- with 3.3 V bias voltage and has 8 output channels with 20 MHz output rate. The developed 10 μm pitch InSb SXGA detector showed median NETD (Noise Equivalent Temperature Difference) of 22.6 mK. To measure the stability of developed 10 _m pitch InSb SXGA detector, system NETD(SNETD) was measured after thermal cycling. The SNETD of 30 mK was measured for more than 200 thermal cycling, which shows that the output of developed FPA is very stable.
Recently, infrared detectors have become increasingly dense and miniaturized. The development of micro solder bumps with small diameter and high aspect ratio is necessary for high pixel density and miniaturized infrared detectors. Indium solder bump has been used for infrared detectors because of its stability at low temperature, electrical conductivity and ductility. In this work, the method and results of forming indium bumps with uniform and high aspect ratio by electroplating is presented. In particular, the electroplating method for forming a uniform micro bump and the method for manufacturing a bump having a uniform height will be presented in detail. Finally, the result of indium bump made of pixel pitch 5 μm and 7.5 μm is presented.
NISS (Near-infrared Imaging Spectrometer for Star formation history) is a unique spaceborne imaging spectrometer (R = 20) onboard the Korea’s next micro-satellite NEXTSat-1 to investigate the star formation history of Universe in near infrared wavelength region (0.9 – 2.5 μm). In this paper, we introduce the NISS H2RG detector electronics, the test configuration, and the performance test results. Analyzed data will be presented on; system gain, dark current, readout noise, crosstalk, linearity, and persistence. Also, we present basic test results of a Korean manufactured IR detector, 640 x 512 InAsSb 15 μm pixel pitch, developed for future Korean lunar mission.
InGaAs detector for SWIR imaging is widely used for remote sensing, medical application, personal identification etc. To reduce the required power for various environmental condition, reducing dark current is crucial. The dark current of InGaAs detector is known to come from defects induced during the growth of wafers and the process to fabricate FPAs. Especially, when high temperature is applied for the diffusion of Zn to form p-type junction on n-type InP/InGaAs substrate, the diffusion barrier of Zn on the substrate experiences large expansion and add stress in the substrate. The induced stress will increase defects and increase dark current. In this work, to reduce the stress of the Zn diffusion barrier, balanced diffusion barrier with multiple layer is applied. By reducing the stress, the dark current density has reduced to below 10 nA/cm2, which is suitable for low power operation.
This paper shows the current status of cooled IR detector technologies at i3system, South Korea. Mass production technology of i3system has successfully supplied lots of QVGA cooled IR detectors to camera customers. i3system has also developed small pitch cooled IR detectors with 320×256 and 640×512 formats for several different applications such as thermal sights and 24-hour operation observation units. In 2013, i3system’s cooled IR detector has been launched in STSAT(Science and Technology SATellite)-2C through Naro-1 program which was South Korea’s first successful launch vehicle for satellite. Owing to i3system’s robust, intensive design and test programs, IR detector technologies have been space qualified without any further efforts by the space program. Currently, development programs for SXGA(1280×1024) with small pitch cooled detector are being progressed and its status is addressed.
Heat-sensitive material is one of the most essential parts of microbolometer fabrication. Vanadium oxide (VOx) and amorphous silicon (a-Si) are widely accepted materials for commercialized focal plane arrays. Meanwhile, there are a lot of efforts for finding alternative materials having better performance, lower process cost and higher yield. In this study, reactively sputtered titanium oxide (TiO2-δ) films were investigated for heat sensitive material. Microbolometer device was also fabricated by using the TiO2-δ film as a heat sensitive material.
It is well known that the TiO2-δ can have several phases according to film deposition condition. Properties of TiO2-δ film could be largely varied by controlling the deposition condition. Resistivity of the fabricated TiO2-δ film was ranged from 10-2 Ω•cm to 10 Ω•cm. Negative TCR(temperature coefficient of resistance) value up to 2.8 %/K was obtained. 1/f noise of the TiO2-δ film was comparable to that of VOx film. From the fabrication result of microbolometer device, feasibility of the reactively sputtered TiO2-δ film was demonstrated. NETD(Noise equivalent temperature difference) of the 50μm-pitch simple single-level membrane structure microbolometer was 34mK with conditions of 1V bias and 30Hz operation frequency.
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.
At present, infrared photodetectors are being increasingly used in space systems, where they are exposed to the space radiation environment. Consequently, the radiation-hardness-related problem in HgCdTe photodetectors has become a critical issue.
In this study, the gamma radiation effects on ZnS- and CdTe-passivated mid-wavelength infrared (MWIR) HgCdTe photodiodes were investigated. Although ZnS has an excellent insulating property, its radiation-tolerant property was revealed very poor in comparison with CdTe. After 1 Mrad of gamma irradiation, the resistance-area product at zero bias (R0A) value of the ZnS-passivated photodiode was drastically reduced by roughly 5 orders from ~107 Ω cm2 to 102 Ω cm2, whereas the CdTe-passivated photodiode showed no degradation in R0A values.
In Korea, Japan and China, the measurement of surface temperature profile shown in abnormalities in neural and vascular functions, facial lesions, changes of blood stream in peripheral tissues (breast cancer, etc.), and psychosomatic problems is widely used for the diagnosis and the progress monitor of disease and symptoms (pains). For this application, single element LWIR Hg0.78Cd0.22Te photo-conductive (PC) detectors were fabricated with the wafers having a cutoff wavelength larger than 12.5 mm. The optical characteristics such as responsivity and detectivity were tested and the operation of the detectors was proved by the thermal imaging system IRIS5000. It was found that the 1/f noise makes lines and seriously degrades the thermal images. MWIR Hg0.70Cd0.30Te photo-voltaic (PV) detectors were also fabricated and tested for the medical application. However, owing to the low signal, the results were far from satisfactory. It is supposed that the integration methods are required for the single element MWIR detector.
Hg0.78Cd0.22Te n on p photovoltaic diodes were fabricated with the wafers grown by liquid-phase epitaxy on CdTe substrate which have a cutoff wavelength of 10.5 micrometer. The wafer was doped with Hg vacancies and the acceptor concentration was 5 X 1015 - 2 X 1016/cm3. We applied the planar ion-implantation technique for the junction formation. Post-implantation annealing was performed to improve reverse bias characteristics and RoA value. Using this method, we obtained RoA values of 2 - 8 (Omega) cm2 at 77 K. However, the increase of RoA by post-implantation annealing saturated as the annealing time increased further. This limit is thought to come from the low minority carrier lifetime in the Hg vacancy doped wafer. To improve the device performance further, we adapted the hydrogenation technique. The RoA of the hydrogenated diode was found to be 70 approximately 120 (Omega) cm2, which is one order of magnitude higher than that of the post-implantation annealed diode. From the model fitting analysis, the hydrogenation effect was attributed to the increase of the minority carrier lifetime.
HgCdTe is the most important material for LWIR detectors, and n on p type with a planar structure using ion-implantation technique is still the state-of-the-art for fabricating infrared focal plane arrays (IRFPAs). Nevertheless, the implantation introduces lattice damage and increases the dark current, which are expected to be reduced by an annealing process. In this paper, HgCdTe diodes ((lambda) coutoff,77k equals 11.0 micrometers) were fabricated on Hg-vacancy doped p type HgCdTe wafers grown on CdTe substrates by LPE, and junction was formed with boron ion-implantation. The annealing process was implemented after the ion-implantation at various temperatures, from 120 degrees Celsius to 200 degrees Celsius, under N2 gas atmosphere. The performance of the annealed diodes was investigated in detail by model fitting analysis. This current model includes four dark current components, i.e. diffusion current, generation-recombination current, trap- assisted tunneling current and band to band tunneling current. Measurements and analyses of 1/f noise characteristics were performed at several bias voltages for samples annealed at 150 degrees Celsius. Among them, both devices annealed for 30, and 60 minutes showed equivalent RoA values, but the latter had lower level 1/f noise current at small reverse bias voltage. From the model fitting analysis, the sample annealed at 150 degrees Celsius for 60 minutes was found to be generation- recombination limited at the small reverse bias while that for 30 minutes was to be trap-assisted tunneling limited. This reduction of 1/f noise was attributed to the decreased trap density in the vicinity of pn junction.
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.
We report the results of annealing effect on the Hg0.78Cd0.22Te diodes fabricated by ion-implantation technique. The annealing was performed after flip-chip bonding with Si substrate. The performances of the diodes, before and after the annealing process, were investigated in detail by model fitting analyses. This model includes five current components, such as diffusion current, generation- recombination current, band to band tunneling current, trap- assisted tunnelling current, and photo current. Especially, in the view of a trap-assisted tunneling mechanism, newly developed model is proposed with the introduction of the Poole-Frenkel effect. Using this model, it is well explained that measured RoA product is much lower than their theoretical values in the ideally diffusion limited or generation- recombination limited cases. By flip-chip bonded annealing, RoA products of the diodes were increased and dark currents were decreased. From the model fitting, the improvements are explained by the change of carrier concentration profile in a p-n junction and the reduction of trap density by the annealing process.