A Miniaturized pH Sensor With an Embedded Counter Electrode and a Readout Circuit

Abstract

Electrolyte insulator semiconductor capacitors (EISCAPs) show a shift in the measured capacitance-voltage (C-V) characteristics with changes in the pH of the electrolyte and has the potential to be used as biosensors. The choice of an electrode to the EISCAP is important for reliable measurements. Here, we discuss a silicon-based EISCAP sensor bonded to a glass wafer with an embedded electrode. Three noble metal electrodes (Pt, Au, Ag) are studied for the ease of integration and performance and it is found that the chloridized Ag electrodes exhibit the highest pH sensitivity and the lowest electrode potential drift with time. A readout system that measures the pH of the electrolyte under test is developed and implemented in a programmable system on chip. Calibration of the EISCAP to account for sensor process variations is also incorporated. The pH measurement data on the miniaturized EISCAPs is presented.Index Terms-Biosensor, bonding, electrode integration, electrolyte insulator semiconductor capacitor (EISCAP), micromachining, miniaturization, pH sensing, thin film Ag-AgCl.

Miniaturized Potentiometric Titration for Improving Portability and Accuracy in the Determination of Total Acid in Squeezed Fruit Juice

“…The size of the sensor was only 25 mm 2 , which permitted diagnosis of the nutrient state of a plant by inserting the sensor into the plant's root. Improvement in design and technology has achieved miniaturization in portable pH sensors (Hammond, Ali, & Cumming, 2005;Kassal, Steinberg, & Steinberg, 2013;Veeramani et al, 2013) by incorporating digital processing (Hammond et al, 2005) and wireless data acquisition (Kassal et al, 2013;Veeramani et al, 2013), which has greatly expanded applicability. Moreover, numerous miniaturized chemical sensors are now commercially available and applicable to practical analyses such as pH, conductivity, ionization, salinity, and multiparameters (Megahed, Hiew, Grünberg, & Constable, 2016;Sakai et al, 2018;Trefz, Lorenz, & Constable, 2018).…”

Miniaturised silicon biosensors for the detection of triglyceride in blood serum

“…The sensors are fabricated using processes similar to those reported previously by us. 20,21 Briey, the silicon wafer aer cleaning using a standard RCA cleaning procedure are bulk micromachined to a depth of 100 mm within masking silicon dioxide windows of dimensions 1.5 mm  1.5 mm. The miniaturised microreactors are electrically isolated from each other by a eld oxide.…”

“…17 Direct readout circuits to calibrate the sensor against process variations and to measure the pH under test have been developed for a large sized EISCAP and a miniaturised EISCAP. 19,20 For the EISCAP sensors we have used a stacked gate dielectric layer of silicon oxide and silicon nitride. While the oxide ensures a better interface with silicon, the silicon nitride layer has better pH sensitivity and is more resistant to electrolyte spoiling.…”

Recent Developments in R.F. Magnetron Sputtered Thin Films for pH Sensing Applications—An Overview

“…In recent years, a number of metal oxides based pH sensors have been developed incorporating IrO2 [16][17][18][19], RuO2 [20][21][22][23][24], PtO2 [25], SnO2 [25], TaO2 [25], TiO2 [25,26] and Ta2O5 [27,28]. pH sensors have been developed using a variety of deposition techniques including magnetron sputtering [20][21][22], sol-gel [17,29], screen-printing [24,30] and plasma enhanced chemical vapour deposition (PECVD) [31,32] and electroplating [33][34][35]. Among the different thin film deposition techniques, magnetron sputtering has become the process of choice for the deposition of a wide range of materials.…”