Research of CMOS biosensor IC for extracellular electrophysiological signal recording and pH value measuring

In this paper an integrated monolithic mixed signal biosensor circuit for both extracellar Electrophysiological signal recording and extracellular solution pH value measuring is designed and researched based on standard 0.6 ¿m CMOS technology. The extracellular bioelectrical signal recording module is consisted of 4×4 active electrical potential sensor array, analog multiplexer, reference sources, digital control circuits and output amplifier. Each sensor unit is 60 ¿m × 60 ¿m in area including a 15 ¿m × 15 ¿m sensing electrode. A correlated double sampling circuit is utilized to remove the common-mode noise. The sensor can linearly amplify signals with peak to peak values from 100 ¿V to 10 mV. The pH sensor module consists of silicon nitride film as pH sensitive layer and field effect transistor with multi-floating gate (MFGFET) structure. The output of the circuit is proportional to the pH value using constant source-drain voltage and current control scheme. The difference of pH-MFGFET and RE-MFGFET is sent to output which reduces the fixed pattern noise existed in the solution and circuits. The testing result shows the pH sensor has an average sensitivity of 35.8 mV/pH for pH1 to pH13 with linearity better than 5%. A temperature sensor with PTAT (Proportional to absolute temperature) is also integrated with this pH sensor. This biosensor can be used for recording bioelectrical activity of in-vitro electrogenic cells. It also can be used for exploring the relationship between cell membrane potential and its nearby solution pH value and temperature.