Silicon-on-Insulator Photoimpedance Sensor Using Capacitance Dispersion

We report on design, fabrication, characterization, and modeling of a photoimpedance sensor employing fully depleted silicon-on-insulator. For a given frequency of measurement, the capacitive impedance shows a high sensitivity to light for a relatively narrow range of the incident power density (approximately two orders of magnitude). Increasing the measurement frequency shifts this range to higher power densities and can be used to tune the sensitivity of the sensor to a certain intensity range. Furthermore, the frequency of measurement can be swept to yield an overall wide dynamic range without sacrificing the sensitivity at individual frequencies. This device could be made a part of the tank of an LC oscillator to emit to a frequency-modulated RF signal in response to illumination.