Abstract
The Ion Sensitive Field Effect Transistor (ISFET) operation based onpolycrystalline silicon thin film transistors is reported. These devices can be fabricated oninexpensive disposable substrates such as glass or plastics and are, therefore, promisingcandidates for low cost single-use intelligent multisensors. In this work we have developedan extended gate structure with PE-CVD Si3N4 deposited on top of a conductor, which alsoprovides the electrical connection to the remote TFT gate. Nearly ideal pH sensitivity(54 mV/pH) and stable operation have been achieved. Temperature effects have also beencharacterized. A penicillin sensor has been fabricated by functionalizing the sensing areawith penicillinase. The shift increases almost linearly upon the increase of penicillinconcentration until saturation is reached for ~ 7 mM. Poly-Si TFT structures with a goldsensing area have been also successfully applied to field-effect detection of DNA.
Highlights
The use of ion-sensitive field effect transistors (ISFETs) as pH sensors has been known for many years [1]
Such Enzyme-modified ISFETs (EnFETs) can in principle be constructed with any enzyme that induces a local change in pH near the surface of the sensor
One distinctive advantage of ISFETs is their suitability for miniaturization, since the signal to noise ratio is independent of the ISFET area
Summary
The use of ion-sensitive field effect transistors (ISFETs) as pH sensors has been known for many years [1]. The sensor response time to VGS change is of the order of 1s, which is due to the Si3N4/electrolyte interface, since the TFT response is much faster. The temperature dependence of the ISFET characteristics has been measured using a 5 mM phosphate buffer with pH 7.6 and it is shown in Fig. 3a for a TFT with W/L = 100 μm/6 μm.
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