UV Imager in TFA Technology
- PDF / 1,923,572 Bytes
- 6 Pages / 384.12 x 617.04 pts Page_size
- 85 Downloads / 178 Views
' Silicon Vision GmbH, D-57078 Siegen, www.siliconvision.de for Halbleiterelektronik, Universitat-GH Siegen, D-57068 Siegen, www.uni-siegen.de/-ihe/
2 Institut
ABSTRACT An image sensor with enhanced sensitivity for near ultraviolet radiation (UVA) has been fabricated in TFA (Thin Film on ASIC) technology. The device employs an amorphous silicon pin detector optimized for UV detection by carbonization and layer thickness variation. The front electrode consists of an Al grid or TCO. Measurements show a peak responsivity of 90 mAW-' at 380 nm. The UV Imager prototype consists of 128 x 128 pixels with a size of 25 [Lm x 25 [tim each, fabricated in a 0.7 [im CMOS process. Global sensitivity control serves to achieve a dynamic range in excess of 80 dB. The sensor can be used in fields such as chemical, medical and astronomical applications. Furthermore, a UV monitor has been developed, suited to warn of excessive sunlight exposure, considering skin type and sun protection factor. INTRODUCTION Amorphous silicon based thin films with fixed or variable spectral sensitivity within the visible light range have been widely employed for image sensors in TFA technology [1]. Due to their vertical integration of detector and circuitry TFA sensors have an inherently higher fill factor than conventional CCD and CMOS imagers. Furthermore, independent optimization of the two components is possible. Generally speaking, the detector system can be further developed after the completion of the ASIC, or vice versa an optimized standard detector can be employed for different sensor types with similar operating conditions. Previous investigations demonstrate that a-Si:H is suited for the fabrication of ultraviolet sensitive detectors likewise [2]. Starting with the fundamental pin structure for a visible light detector, bandgap engineering and thickness variation allow to shift the spectral sensitivity to the near UV range. UV optimized detectors employing aluminium or TCO front electrodes have been fabricated and evaluated. While "solar blindness" as postulated in [3] would be useful in case a broadband light source is employed, filters are necessary to suppress visible light in practical applications. The availability of a-Si:H detectors optimized for the UV range and qualified filters allows the fabrication of TFA sensors for a variety of medical, biotechnical and astronomical imaging applications. The first section of this paper describes the device structures and properties of UVA optimized a-Si:H detectors with aluminium and TCO front electrodes. In the second section a UV imager in TFA technology is presented, based on the design of a previously developed visible light sensor. A specialized UV monitor for the control of sunlight exposure is outlined in the subsequent section. UV SENSITIVE THIN FILM DETECTORS The UHV cluster system for PECVD depicted in Fig. I allows to fabricate a variety of highquality amorphous silicon based thin film detectors. A pin layer system with an i-layer thickness of 0.5 - 1 jim exhibits a maximum sensiti
Data Loading...
