An electrical characterisation system for the real-time acquisition of multiple independent sensing parameters from organic thin film transistors

Abstract

Abstract. The presence of multiple independent sensing parameters in a single device is the key conceptual advantage of sensor devices based on an organic thin film transistor (OTFT) over simple organic chemiresistors. Practically, however, these multiple parameters must first be extracted from the electrical characteristics of the OTFTs and, thus, they are not immediately apparent. To exploit the advantage of OTFT sensors, we require a measurement technology to extract these parameters in real time. Here, we introduce an efficient, cost-effective system that is a faster and more compact alternative to the expensive and cumbersome laboratory-based instruments currently available. The characterisation system presented here records the electric behaviour of OTFTs in the form of its "saturated transfer characteristics" multiple times per second for virtually unlimited periods of time, with the option to multiplex up to 20 devices in parallel. By applying a bespoke algorithm to the measured transfer characteristics, the system then extracts, in real time, several underlying transistor parameters (on-and off-current, threshold voltage, and charge carrier mobility). Tests were conducted on the example of a poly(thieno[3,2-b]thiophene) (PBTTT) OTFT exposed to ethanol vapour. The system extracts the underlying OTFT parameters with very low noise without introducing apparent correlations between independent parameters as an artefact.

A water-gated organic thin film transistor as a sensor for water-borne amines

“…In this setup, a positive source voltage is equivalent to a grounded source with negative and equal gate-and drain voltages in a conventional semiconductor parameter analyser, and will turn a hole-transporting OTFT 'on' into drain current saturation when threshold is exceeded. We have described this characterisation scheme in detail in an earlier publication [17]. Gating is affected across water as this acts as electrolyte, as previously described by Berggren et al [10].…”

Bias Stress in Organic Thin-Film Transistors Towards Low-Cost Flexible Gas Sensors

“…As a consequence, even devices with a high-quality semiconductor/dielectric interface suffer from bias stress (BS) effects [28]. That is the reason why, in the past five years, most OTFT-based sensors were built on Si substrate with evaporated source and drain electrodes through a shadow mask [3,[9][10][11][12][14][15][16][17][18][19].…”

“…Bottom source and drain contacts, on the other hand, make it possible to pattern the electrodes and, consequently, pack more transistors in less substrate area as in electronic noses (e-noses) [2,4]. Since the morphology of an organic semiconducting thin-film can be easily altered by organic solvents, patterning electrodes on top of such a film usually demands an orthogonal photoresist [5,6], microcontact printing [7] or, as done by most research groups in the past five years, metal evaporation through a shadow mask [3,[8][9][10][11][12][13][14][15][16][17][18][19].…”

Stability of Polythiophene-Based Transistors upon Bending for Gas Sensing Applications

“…In order to take this next step, the dielectric film must withstand semiconducting film deposition, as well as source and drain patterning. That is the reason why, even nowadays, the vast majority of FET-based sensors are built on oxidized Si wafers with source and drain electrodes evaporated through a shadow mask [12,14,17,[19][20][21][22][23][24]33]. Cross-linked polyvinyl phenol (PVP) on plastic substrates is a good candidate to replace brittle highly-doped Si [37].…”

“…It is worth noting that most recently developed polythiophene-based TFTs as gas sensors still use hard substrates (e.g. Si and glass) [11][12][13][14][15][16][17][18][19][20][21][22][23][24] and rarely study performance upon bending or stretching [25]. This research will be the basis for future studies on flexible polythiophene-based FETs as gas sensors.…”