ISFET Pixel Array With Selectable Sensitivity and Bulk-Based
Offset-Drift Nullification Capability for Reduction of Non-Ideality
Effects
Abstract
This paper presents a monolithic, cost-effective, label free, low power,
robust 3x2 fully differential ISFET pixel array aimed at pH sensing.
Each pixel is based on a differential readout architecture which
eliminates need for additional non-ideality compensation circuitry.
Additionally, the design offers the capability to correct for residual
drift and trapped charge offset through substrate-based voltage
adjustment during calibration. The design also provides a unique ability
for selecting pH sensitivity according to the desired mode of operation
which has not been demonstrated previously. We present experimental
results obtained from the pixel array fabricated in an unmodified AMS
0.35μm CMOS process using a 3.3V power supply. Each pixel demonstrates a
differential sensitivity of 61mV/pH when operated in high sensitivity
mode and 25mV/pH when operated in high non-ideality rejection mode over
the entire pH range, with the ability to remove the already small drift
of 0.3 mV/min and any offset mismatch by adjusting the substrate
voltage