Lately IRnova's research activities have been focused on the development of its next generation Type II Superlattice (T2SL) and Quantum Well Infrared Photodetector (QWIP) based infrared focal plane arrays (FPA) and Integrated Detector Dewar Cooler Assembly (IDDCAs) with 640x512 pixels @ 15μm pixel pitch. Last year we presented the initial results obtained for both of the above mentioned technologies at FPA and single element level. In this paper we will introduce our next generation of fully functional IDDCA (@15μm pixel pitch) solutions for MWIR and LWIR detection based on T2SL and QWIP technology respectively. Novelty of these IDDCAs lies in that fact that both of these products make use of FLIR indigo's ISC0403, and similar Cooler and Dewar assemblies. Performance in terms of picture quality, operability, response uniformity, stability and NETD of these IDDCAs is evaluated using demonstrator cameras developed in-house. This QWIP based LWIR IDDCA is the smallest pixel pitch commercially available IDDCA using this technology.
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.
This paper reviews the development history and current status of HgCdTe based IR detector of which the study had
started from 1980's in South Korea. It covers the fields from single element diode to 2-dimensional IR detector as well as
dewar technology. The past studies of large area single element diode, linear array detector, 2-D IRFPAs are reported
which include HgCdTe diode array, ROIC and hybridization technologies. Thanks to the sound cooperation between
academia, research institute, industry, and government, current progress of 2-D IR detector shows high performance and
reliability to be able to be utilized in fields. Finally, prospective future of IR detector in Korea is addressed.
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.
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.
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.
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.
We have made nanoscale fabrication for HgCdTe-based Coulomb blockade type quantum devices. Using e-beam lithography and lift-off technique with ZEP resist, multi-lines with 0.1/0.3 nm width and space were nano-patterned on ZnS/HgCdTe surface. SEM and AFM images for the lines display well-splitted patterning result with a little roughing ZnS surface. Split- gate of 200 nm radius was also fabricated on ZnS/MCT for defining nanosize quantum dot. All the work will provide a fundamental basis for the nanofabrication process of HgCdTe- based narrow-gap quantum devices.
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.