High photocurrent and operation frequency for light-addressable potentiometric sensor by thinner Si substrate

LAPS with different thickness of P-type silicon wafers are first investigated for photocurrent, operation frequency of applied ac signal and pH sensing performance, respectively. A high dielectric constant material, niobium oxide (NbO_x), was directly deposited as the sensing membrane by reactive radio frequency sputtering. pH sensitivity is around 60.3 mV/pH with linearity of 99.1%. Thin Si substrate has higher photovoltage, especially with high-frequency ac signal. With ac signal of 20kHz, photovoltage of 350 um Si shows comparable to 500 um Si. Even in frequency higher than 50 kHz, fast scanning speed could be achieved by analog mirror and red laser for chemical image sensor.