Development of Thin Film Radiation Detectors using TiO_2 film by plasma CVD method

采用50 Hz等离子体增强化学气相沉积技术，以TiCl4+O2混合气体为衬底，用两个二极管作为衬底偏置电路，在600℃的条件下在氧化铝衬底上沉积了二氧化钛薄膜。衬底偏压为-50(V)，气体混合比(TiO2/O2)为0.05。薄膜的折射率、介电常数和光学能隙分别约为2.7、120和3.0。利用等离子体化学气相沉积技术在厚度为1 mm的氧化铝基片上沉积了厚度为100 nm~1μm的二氧化钛薄膜。看来，二氧化钛的厚度对探测器的S/N特性有影响。在外加电压为10(V)的情况下，2 0 0(Nm)厚的TiO2/氧化铝结构的探测器暗电流为几十pA，1(μm)厚度的二氧化钛/氧化铝结构的探测器暗电流很小。因此，我认为二氧化钛的厚度最好小于100 nm左右。在二氧化钛/氧化铝结构上放置两个金膜电极，在两个电极之间添加1：100(V)。胶片探测器分别用曝光率为2~8(C/kg/min)和5~33×10~(-4)(C/kg/min)的γ射线和X射线照射。用静电计在外加电压10(V)下测量了I=5(PA)~300(PA)的辐照电流。测得的辐照电流与辐照强度呈线性关系。辐射检测灵敏度约为60nA/(C/kg/min)。由此可见，二氧化钛/氧化铝结构的薄膜辐射探测器可以测量γ-射线和X射线的强度。此外，该探测器还可以实现5×5×1(Mm)的小尺寸。此外，碳化硅/氧化铝结构比二氧化钛/氧化铝结构具有更低的暗电流。因此，与二氧化钛/氧化铝结构相比，碳化硅/氧化铝结构是一种较好的探测器。

The TiO_2 film have been deposited on alumina substrate by the 50Hz plasma-enhanced CVD at 600℃ using TiCl_4+O_2 gas mixture with a substrate bias circuit using two diodes. Substrate bias voltage was -50(V), and the gas mixture ratio (TiO_2/O_2) was 0.05. The refractive index, dielectric constant and optical energy gap were about 2.7, 120 and 3.0, respectively.Thin film Radiation detector was made by TiO_2/alumina structure. TiO_2 on alumina plate (1mm in thickness) was deposited 100(nm) to 1(μm) in thickness by the plasma CVD. It seems that thickness of TiO_2 influence upon detector S/N characters. Detector dark current at TiO_2 thickness 200(nm) of TiO_2/alumina structure by 10(V) applied voltage was few tens pA, 1(μm) thickness TiO_2/alumina was few nA current. Therefore, I think so that the thickness of TiO_2 is better than less about 100(nm). Gold thin film two electrodes were set on TiO_2/alumina structure, and add 1 to 100(V) between two electrodes. The film detector was irradiated γ-ray and X-ray of exposure rate 2〜8(C/kg/min) and 5〜33×10^<-4>(C/kg/min), respectively. Irradiation current of I=5 (pA) to 300(pA) was measured with an electrometer at applied voltage 10(V). The measured irradiation current has linearity against radiation intensity. And detection sensitivity of radiation was about 60(nA/ (C/kg/min)). Accordingly, it appears that the thin film radiation detector of TiO_2/alumina structure can be measuring intensity of γ-ray and X-ray. Moreover, the detector was made possible small size as 5×5×1(mm). Moreover, SiC/alumina structure has lower dark current than that of TiO_2/alumina structure. Therefore, it seems that SiC/alumina structure was good detector in comparison with TiO_2/alumina structure.