CCD紫外敏感Lumogen薄膜制备与光谱表征

传统的CCD和CMOS成像传感器对紫外区域响应比较弱,这是因为多晶硅栅对紫外光有强的吸收能力,从而阻碍了紫外光进入CCD沟道。为了提高探测器对紫外辐射的敏感性,可行的一种办法是在器件上镀一层可以将紫外光转化为可见光的变频膜。采用真空蒸发法制备了有机Lumogen薄膜,并用发光官能团分析、椭圆偏振技术研究了Lumogen薄膜的发光原理与光学常数。分析与实验结果表明：Lumogen可连续光致发光原因是其分子具有四类双键结构;椭圆偏振法测得该Lumogen薄膜折射率在1.3左右,说明该膜具有增透效果。同时,通过测量Lumogen薄膜的透射光谱、吸收光谱、光致发光发射谱和激发谱,表征了Lumogen薄膜的光谱性质,发现Lumogen薄膜在可见波段(>470 nm)有较好的透过性,用紫外光激发会产生较强的黄绿光(中心波长位于523 nm),且激发光谱宽(240～490 nm)。结论表明Lumogen薄膜的发射光谱能够与CCD等传统硅基成像器件的响应光谱匹配,是一种符合实际要求的紫外敏感薄膜。

Preparation and Spectral Characterization of Lumogen Coatings for UV-Responsive CCD Image Sensors

Traditional charge-coupled devices (usually front-illuminated CCDs) and complementary metal oxide semiconductor (CMOS) have lower response in ultraviolet region particularly.The reason is that polysilicon gate material absorbs the ultraviolet radiation highly,which leads to a barricade of the radiation penetrating the gate to the channel of CCD.To enhance the detective responsibility of CCD in the ultraviolet region,a feasible method is to coat the surface of CCD polysilicon gate with a thin film.The thin film should have the ability of converting the ultraviolet to visible in order to enable the UV radiation to penetrate the polysilicon gate.An organic coating to convert the UV radiation to visible has been developed in the present paper.Lumogen thin films were deposited on fused silica substrates by vacuum evaporation of an organic dye called Lumogen(R) Yellow S0790.Analysis of organic functional groups was used to study the luminescence mechanism of Lumogen.The optical constants of coatings were calculated by spectroscopic ellipsometry.The results indicate that Lumogen exhibits photoluminescence continuously owing to four kinds of double bonds in each Lumogen molecule.The refractive index of Lumogen film was～1.3,which indicates that this film could be considered an antireflection coating.Finally,the spectral properties of Lumogen coatings were characterized by transmission,absorption,photoluminescence emission,and excitation spectra.It is showed that these coatings were transmitted well in visible region (λ＞470 nm),and emitted a yellowish green glow centered at～523 nm together with a wide excitation spectrum field from 240 nm to 490 nm.The synthesis shows that Lumogen coatings match accurately with the detected spectrum of conventional silicon-based image sensors,which makes this kind of thin films an ultraviolet responsive coating for sensors.