Abstract
This paper presents a MOSFET based biosensor circuit for the monitoring of such things as creatinine in patients with renal failure. Its VLSI layout is presented for 1.2 mu or for 2.0 mu MOSIS CMOS processes. The proposed biosensor circuit is a capacitive gap sensor where the device consists of a bridge made of three standard PMOS devices connected either as resistors or capacitors and forming three arms of the bridge. The fourth arm is a similar PMOS transistor but with a gap between the channel and a raised poly layer in which a fluid, such as creatinine, or a gas, can be placed. PSpice simulations and Spice extractions from the layout are included to demonstrate the operation of the circuit.