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.
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.