Large area p-i-n flexible image sensors
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I7.11.1
Large area p-i-n flexible image sensors 1
M. Vieira, 1P. Louro, 1M. Fernandes, 1R. Schwarz, 2M. Schubert. Electronics Telecommunications and Computer Dept, ISEL, Lisbon, Portugal 2 Institut IPE, Universitat Stuttgart, Pfaffenwaldring 47, D-70569, Stuttgart, Germany 1
ABSTRACT Large area p-i-n image sensors deposited on plastic substrates were produced at low temperatures (110 ºC) by PE-CVD and compared with similar sensors deposited on glass substrates. The same sensing element structure ZnO:Al/p(SiC:H)/i(Si:H)/n(SiC:H)/Al was used for both devices. In this work the efforts are focused mainly on the optimization of the output characteristics of the sensor when fabricated on plastic substrates. The role of the sensor configuration and readout parameters in the image acquisition process is analyzed. The opticalto-electrical transfer characteristics show a reasonable quantum efficiency under a red light pattern, broad spectral response, and reciprocity between light and image signal. First results show that the sensors deposited on flexible substrate present smaller light to dark sensitivity than those deposited on glass. In both, the non ohmic behavior of the transparent conductive oxide front contact blocks the carrier collection and leads to a surprising linear dependence of the image signal with the applied voltage. INTRODUCTION Electronics on flexible substrates is becoming more and more interesting for flexible displays, sensor arrays, curved circuits, curved detector arrays, mechatronic materials, sensor skins, and other large-area electronics [1, 2, 3]. The plastic substrate provides devices that are lighter in weight and more resistant to impact damage, making them suitable for portable devices. Large area a-SiC:H imagers fabricated on plastic substrates are strong candidates for flexible electronic. They can be manufactured, at low cost, taking advantage of the amorphous silicon technology. In our group large area hydrogenated amorphous silicon single and stacked p-i-n structures with low conductivity doped layers were deposited on glass covered substrates and proposed as image sensors [4, 5, 6]. These sensors are different from the conventional ones [7, 8, 9], since they are based on one single or stacked sensing element and use a modulated, lowpower laser beam to scan and acquire the image directly. The photocurrent generated by the moving beam is recorded as the electronic image signal, and its magnitude depends on the light pattern position, wavelength and intensity. Advantages to this approach are large area imaging, high resolution, and uniformity of measurement along the sensor. This work evaluates the possibility of using a single p-i-n device deposited on plastic as an optically addressed read-write image-processing device. Efforts are focused mainly on the optimization of the sensor performance (contrast and resolution). A trade-off is established between sensor design and light pattern and scanner wavelengths. SENSOR OPERATION The imager is an optically addressed read-write device based
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