Integrated CMOS ISFETs
We are living in an era where advances in silicon-based technologies are driven by the requirements of computing and mobile communications. In recent years however, the growing needs of society to improve on healthcare and quality of life have seen integrated circuits offering novel solutions for various biomedical applications. As a result there is a new drive for these technologies to be applied in healthcare, to provide cheap, disposable, low power and intelligent systems to provide diagnosis and treatment of medical conditions.
In order for any chemical sensor to be monolithically integrated on a single chip to make such systems, it must be implementable within the same technology on which the circuits are made. CMOS-based integrated circuits are getting smaller and lower in cost as a result of the decreasing feature size of the MOSFET, and the economies of scale of semiconductors. Implementing chemical sensors in CMOS has therefore been an avidly pursued research area due to the overlapping requirements of modern day chemical micro-sensing devices. These include miniaturisation of sensors, batch fabrication and incorporation of processing and signal conditioning circuitry to improve signal to noise ratio, implement intelligent algorithms and conserve power.
ISFETs are ion selective chemical sensors which can be fabricated in CMOS using standard MOSFETs and the native passivation of the CMOS process. They are usually referred to as ISFETs in unmodified CMOS. For applications of pH sensing this requires no extra processing steps to deposit the membrane and can be used unmodified using an external reference electrode. From thereon making the devices selective to other ions requires deposition of other membranes. This has made the ISFET an attractive option because it can take full advantage of the merits which come with implementation in a standard CMOS process which include miniaturisation, repeatability, minimal process variation, high yield and low cost of large volumes.
This research involves developing novel Lab-on-chip technologies utilising Ion-sensitive field effect transistors. Current ongoing research uses these for real time DNA SNP detection for point of care medical applications. Additional applications include detection of glucose for diabetes, detection of creatinine and urea as a determinant for renal function and detection of potassium and sodium for Neuronal monitoring.
1. Y Liu, P Georgiou, T Prodromakis, TG Constandinou, C Toumazou, "An Extended CMOS ISFET Model Incorporating the Physical Design Geometry and the Effects on Performance and Offset Variation", IEEE Transactions on Electron Devices, Vol. 58, pp. 4414-4422, 2011.
2. ZDC Goh, P Georgiou, TG Constandinou, T Prodromakis, C Toumazou, "A CMOS-Based Lab-on-Chip Array for Combined Magnetic Manipulation and Opto-Chemical Sensing", IEEE International Symposium on Circuits and Systems (ISCAS), pp. 1997-2000, 2011.
3. T Prodromakis, Y Liu, TG Constandinou, P Georgiou, C Toumazou, "Exploiting CMOS Technology to Enhance the Performance of ISFET Sensors", IEEE Electron Device Letters, Vol. 31, pp. 1053-1055, 2010.