Tunable and Wireless Photoimpedance Light Sensor
- PDF / 699,459 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 104 Downloads / 164 Views
Tunable and Wireless Photoimpedance Light Sensor
Tanuj Saxena1, Sergey Rumyantsev1, Partha Dutta1 and Michael Shur1,2 1
Department of E.C.S.E, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
2
Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy
NY 12180, USA
ABSTRACT We report on the effects of the frequency dispersion in light sensitive materials used in photoimpedance wireless sensors. An example of such a sensor is a gated semiconductor connecting two or more fixed capacitances. The impedance of the device under illumination is changed by the change in the photoresistance of the semiconductor layer and the change in the gate-semiconductor capacitance. We report on the design and simulation of the frequency dispersion of the impedance of this device in silicon and discuss the physics and device performance. We also evaluate the dynamic range and sensitivity of the wireless photoimpedance sensors and show their advantages for wireless sensing applications compared to more conventional light sensors. INTRODUCTION The emergence of LED based intelligently controlled lighting systems stimulated growing interest in versatile wireless sensors capable of color discrimination and having a wide dynamic range and high sensitivity. In this paper, we report on photocapacitive sensors utilizing the frequency dispersion for expanding the dynamic range. Such sensors can easily be integrated into wireless RF circuits. Conventional photocapacitive devices like Schottky diodes [1, 2] work only on change in trap occupancy in the space charge region under illumination, which is usually small. Demonstrated MOS photocapacitors [3-5] use the modulation of inversion layer under illumination. We propose a novel design, which utilizes the physical mechanisms changing both active and imaginary device impedance (i.e. resistance and capacitance). This sensor design consists of two or more fixed capacitances connected by the light and frequency sensitive elements. We have demonstrated such a concept using a cadmium sulfide device [6]. In this report, we present the simulation results for a related but different structure implemented in silicon. DEVICE DESIGN Fig. 1. Shows the device design that consists of fixed capacitors (geometric capacitors) monolithically integrated with photosensitive elements - a metal-oxide-semiconductor (MOS) capacitance and semiconductor photoresistance. The bottom plates of the geometric capacitances
sit directly on the semiconductor substrate and are separated from the top plates by a dielectric film. The top plates of the geometric capacitances and the gate of the MOS capacitor structure are tied together to form the gate terminal of the device. The second terminal of the device is the substrate of the MOS structure. A narrow metal line directly under the gate serves as the substrate contact. Illumination leads to changes in the MOS capacitance and in the reduction of the resistance between the substrate contact and the bottom plates of the geometric capacitanc
Data Loading...
