Research Interests

Over the previous 10 years Dr Covington has been developing novel chemical sensors, sensing materials and micro-systems. These components are common in many gas detectors and so called ?Electronic Noses? that mimic the human olfactory system. These systems are used, for example, in the odour identification of environmental pollutants, medical diseases and explosives. Much of his work has been focussed on creating CMOS compatible sensor and sensor systems for mass market applications, for example, investigating SOI CMOS compatible micro-hot plates and chemFET sensors.More recently work has focussed more towards bio-medical applications of these systems developing low cost rapid analysis of diseases. Below is a summary of some of the research areas in which Dr Covington is presently active in.

High temperature micro-hot plates

One area of interest has been the development of high temperature micro-hot plates. Many gas sensitive materials require elevated operating temperatures to detect poisonous gases. Here at Warwick we are developing high temperature micro-hot plates based on MOSFET and Tungsten heaters embedded in a membrane formed from the silicon layer of an SOI wafer (Silicon-On-Insulator). Such devices are fully CMOS compatible and so can be fabricate using standard CMOS processing techniques and hence be low cost. In addition, the buried oxide layer makes back-etching process much simpler. Here we have shown MOSFET Heaters operating up to 350 ^oC and tungsten resistive heaters up to 700 ^oC for mW power consumption. Such micro-heaters have considerable lower power consumption and higher operating temperatures than many other CMOS compatible commercial or research micro-hot plates.

Biological Inspired Chemical Sensing Micro-system

In further work we are attempting to mimic the human olfactory system to develop an electronic nose that can solve more challenging odour discrimination problems. Here we have developed a front-end microsystem which has been inspired by the human olfactory mucosa. The mucosa is the mucus coating and receptor cells inside the nasal cavity. This mucus layer behaves as a ?nasal chromatograph? similar to the gas chromatograph. This has been fabricated using Microstereolithography and been post-coated with an artificial mucus layer. Our ?nasal chromatograph? has been integrated with a silicon based sensor array on which the micro-package sits. Thus such a system gives both spatial and temporal information. This temporal information arises as the artificial mucus layer behaves as a retentive layer slowing the progress of certain odours through the micro-fluidic system. This delay depends upon the molecule hence pulses of different chemicals will reach the sensors at different times, aiding discrimination.

Further work on this idea is now progressing looking into using much larger sensor numbers and creating a measurement micro-system by combining these ideas together. It is hoped to use this completed system for a number of bio-analysis applications.

Blood sampling and analysis

The sampling and analysis of blood costs the NHS millions of pounds and year. In addition needle and stick injuries pass on many infections to staff within the NHS and medical profession. Here at Warwick we are developing painless methods of sampling and analysing blood. These sampling devices are designed to be painless, low cost and disposable. The painless method of blood sampling is based on a micro-needle array, which is so small that the patient does not feel the sampling process. In addition, we are investigating methods of analysing the blood for a number of conditions. Again, these devices are being fabricated using micro stereo-lithography techniques, employing a range of bio-compatible and bio-degradable materials. In the future we hope to combine both the sampling and analysis system to create a complete low cost device. An SEM picture of a micro-needle array is shown below.

ChemFET sensors and CNT sensing materials

Another area of interest has been the development of chemical FET devices. Here the standard gate metal is replaced with a conducting chemical sensing material, usually a conducting polymer. This work has concentrated on room temperature sensors, hence have the ability for low-power operation with CMOS integration. Further work has concentrated on using FET sensors combined with resistive sensors to form a combined sensor. Hence we can measure change in resistance and workfunction of the sensors as the same time. A photograph of such a device is given below. This work is has also combined the Carbon Nano-Tubes (CNTs) with polymer for both resistive and FET sensors. The purpose of which is to create sensors with higher sensitivity, diversity and stability.