Organic Thin-film Transistor Sensors Research Articles

Formaldehyde Gas Sensor Based on Pentacene Organic Thin-Film Transistor

Formaldehyde (HCHO) gas sensors based on pentacene active layer and low cost poly (merthyl methacrylate) (PMMA) insulator were fabricated with a structure of bottom contact organic thin-film transistor (OTFT). The OTFT sensor not only presented a remarkable response characteristic in the absence and the presence of HCHO gas with different concentrations, but also exhibited a good repeatability for sensing the HCHO gas. Meanwhile, compared to the device operated in nitrogen circumstance, obvious changes in saturation drain-source current (IDS) and off-state current were observed when the device exposed to HCHO gas. Also the device performance and sensing mechanisms were discussed.

Development of a Novel Formaldehyde OTFT Sensor Based on P3HT/Fe2O3 Nanocomposite Thin Film

The formaldehyde (HCHO) is considered as a major cause of sick building syndrome (SBS). The majority of conventional HCHO sensors have some drawbacks such as sensitivity, long sampling time and high operating temperature. In this report, a novel organic thin film transistor (OTFT) HCHO sensor based on poly-3-hexylithiophene (P3HT)/ferric oxide (Fe2O3) nanocomposite thin films was developed by the spraying process. The results showed that the P3HT/Fe2O3 nanocomposite thin film OTFT sensor has the improved response and reproducibility compared with the single P3HT thin film OTFT, which may be ascribed to porous surface morphology of the nanocomposite thin film partially.

Flexible spray-coated TIPS-pentacene organic thin-film transistors as ammonia gas sensors

Flexible ammonia (NH3) gas sensors based on solution-processable organic thin-film transistors (OTFTs) are fabricated using a TIPS-pentacene active layer/PMMA dielectric layer on glass and plastic substrates. These OTFT sensors exhibit outstanding NH3 gas response and recovery characteristics under multiple exposure/evacuation cycles at controlled NH3 concentrations.

Organic Thin-Film Transistors for Selective Hydrogen Peroxide and Organic Peroxide Vapor Detection

Direct selective detection of hydrogen peroxide and di-tert-butyl peroxide vapors was demonstrated using organic thin-film transistor (OTFT) threshold voltage shifts. Positive threshold voltage shifts are observed during peroxide vapor sensing for metal–phthalocyanine (MPc)- and naphthalocyanine (Nc)-based OTFTs. The positive threshold voltage shift observed for peroxides is not evident with nonoxidizing analytes such as dimethyl methylphosphonate (DMMP) and water. MPc and Nc OTFT sensors operating at room temperature have distinct responses in mobility and threshold voltage to peroxide vapors. The mobility changes are reversible under dry air flow, whereas positive threshold voltage shifts are reversed by counter-dosing with a polar, electron-donating analyte. The peroxide-induced threshold voltage shifts suggest an accumulation of positive charge in the MPc/Nc film. The results are consistent with a dual-response mechanism in which the peroxide molecularly chemisorbs and subsequently catalytically decom...

Analyte selective response in solution-deposited tetrabenzoporphyrin thin-film field-effect transistor sensors

Organic thin film transistor (OTFT) chemical sensors rely on the specific electronic structure of the organic semiconductor (OSC) film for determining sensor stability and response to analytes. The delocalized electronic structure is influenced not only by the OSC molecular structure, but also the solid state packing and film morphology. Phthalocyanine (H 2Pc) and tetrabenzoporphyrin (H 2TBP) have similar molecular structures but different film microstructures when H 2Pc is vacuum deposited and H 2TBP is solution deposited. The difference in electronic structures is evidenced by the different mobilities of H 2TBP and H 2Pc OTFTs. H 2Pc has a maximum mobility of 8.6 × 10 −4 cm 2 V −1 s −1 when the substrate is held at 250 °C during deposition and a mobility of 4.8 × 10 −5 cm 2 V −1 s −1 when the substrate is held at 25 °C during deposition. Solution deposited H 2TBP films have a mobility of 5.3 × 10 −3 cm 2 V −1 s −1, which is consistent with better long-range order and intermolecular coupling within the H 2TBP films compared to the H 2Pc films. Solution deposited H 2TBP also exhibits a textured film morphology with large grains and an RMS roughness 3–5 times larger than H 2Pc films with similar thicknesses. Despite these differences, OTFT sensors fabricated from H 2TBP and H 2Pc exhibit nearly identical analyte sensitivity and analyte response kinetics. The results suggest that while the interactions between molecules in the solid state determine conductivity, localized interactions between the analyte and the molecular binding site dominate analyte binding and determine sensor response.

The response characteristics of a gas sensor based on poly-3-hexylithiophene thin-film transistors

This paper studies the response characteristics of a gas sensor for organic thin-film transistors (OTFTs), made from spin-coated poly-3-hexylthiophene (P3HT) on a thermally grown SiO2/Si wafer. The gas response characteristics of OTFT sensors are observed from the change in the drain–source current, as a function of time, when the P3HT-based OTFT sensors of different channel widths are exposed to cycles of exposure to and the evacuation of NH3 gas, with concentration ranging from 10 to 100 ppm at room temperature in normal atmosphere. The measured drain–source current decreases rapidly with time after exposure to NH3 gas and the response characteristics of the drain–source current are seen to be higher for larger values of NH3 gas concentration. Also, the response characteristics of the OTFT sensor show that there is a shift in the threshold-voltage as well as a change in mobility after exposure to NH3 gas.

Material and device considerations for organic thin-film transistor sensors

The rapid development of the field of organic electronics has sparked great interest in the use of organic thin-film transistors (OTFTs) as low-cost electronic sensors. The direct coupling of the electronic and the sensor media to provide real time electrical output has already demonstrated high sensitivity to a variety of chemical species. The synthetic versatility of organic materials also provides endless routes to impart functionality for specifically targeted chemical interactions. Owing to their compatibility with flexible materials and simple fabrication methods, OTFTs are poised to have a tremendous impact on future portable detection technology. This article reviews recent progress made toward improved sensitivity, selectivity and stability of OTFT sensors through material and device engineering. Specific consideration is paid to the interaction of the electronic materials with the analytes as a means of providing insight into mechanistic principles as well as the future direction of OTFTs.

Contact effects in organic thin-film transistor sensors

Contact effects in organic thin-film transistors (OTFTs) sensors are here investigated specifically respect to the gate field-induced sensitivity enhancement of more than three orders of magnitude seen in a DHα6T OTFT sensor exposed to 1-butanol vapors. This study shows that such a sensitivity enhancement effect is largely ascribable to changes occurring to the transistor channel resistance. Effects, such as the changes in contact resistance, are seen to influence the low gate voltage regime where the sensitivity is much lower.

Water-stable organic transistors and their application in chemical and biological sensors

The development of low-cost, reliable sensors will rely on devices capable of converting an analyte binding event to an easily read electrical signal. Organic thin-film transistors (OTFTs) are ideal for inexpensive, single-use chemical or biological sensors because of their compatibility with flexible, large-area substrates, simple processing, and highly tunable active layer materials. We have fabricated low-operating voltage OTFTs with a cross-linked polymer gate dielectric, which display stable operation under aqueous conditions over >10(4) electrical cycles using the p-channel semiconductor 5,5'-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2'-bithiophene (DDFTTF). OTFT sensors were demonstrated in aqueous solutions with concentrations as low as parts per billion for trinitrobenzene, methylphosphonic acid, cysteine, and glucose. This work demonstrates of reliable OTFT operation in aqueous media, hence opening new possibilities of chemical and biological sensing with OTFTs.

A sensitivity-enhanced field-effect chiral sensor

Organic thin-film transistor sensors have been recently attracting the attention of the plastic electronics community for their potential exploitation in novel sensing platforms. Specificity and sensitivity are however still open issues: in this respect chiral discrimination-being a scientific and technological achievement in itself--is indeed one of the most challenging sensor bench-tests. So far, conducting-polymer solid-state chiral detection has been carried out at part-per-thousand concentration levels. Here, a novel chiral bilayer organic thin-film transistor gas sensor--comprising an outermost layer with built-in enantioselective properties-is demonstrated to show field-effect amplified sensitivity that enables differential detection of optical isomers in the tens-of-parts-per-million concentration range. The ad-hoc-designed organic semiconductor endowed with chiral side groups, the bilayer structure and the thin-film transistor transducer provide a significant step forward in the development of a high-performance and versatile sensing platform compatible with flexible organic electronic technologies.

Ultralow drift in organic thin-film transistor chemical sensors by pulsed gating

A pulsed gating method has been developed to enhance the baseline stability of organic thin-film transistor (OTFT) chemical sensors. Trap states in the organic films are the major source of the OTFTs baseline drift under static gate bias, which is identified as the bias stress effect (BSE). BSE typically reduces the baseline current by 60% over 20h in phthalocyanine based OTFT sensors. The baseline drift has been reduced below 1% over 20h in the absence of the analyte using the pulsed gating method. With pulsed gating, the baseline drift on exposure to 15 methanol pulses is less than 0.09%∕h, and the response to this analyte is fully recoverable. Similar ultralow drift results were obtained for methanol sensing on three different phthalocyanine OTFTs. Combining the pulsed gating with low duty cycle analyte pulses, this method is also applicable to obtain ultralow drift (0.04%∕h) even for low vapor pressure analytes such as organophosphonate nerve agent simulants.

Effect of morphology on organic thin film transistor sensors

This review provides a general introduction to organic field-effect transistors and their application as chemical sensors. Thin film transistor device performance is greatly affected by the molecular structure and morphology of the organic semiconductor layer. Various methods for organic semiconductor deposition are surveyed. Recent progress in the fabrication of organic thin film transistor sensors as well as the correlation between morphology and analyte response is discussed.

Organic thin-film transistor sensors: Interface dependent and gate bias enhanced responses

Organic thin film transistors are a new class of sensors potentially capable of outperforming chemiresistors. They can be operated at room temperature, offer the advantage of remarkable response repeatability and can function as multi-parameter sensors. In this paper, evidence of OTFT response dependence on important parameters such as the chemical nature of the organic semiconductor active layer and the gate-dielectric/organic-semiconductor interface are produced. A sizable response enhancement of an OTFT sensor operated in the enhancement mode is also presented indicating that an OTFT can in principle lead to a lower detection limit than a resistor-type sensor with the same organic semiconductor.

Organic TFTs as gas sensors for electronic nose applications

The use of organic thin-film-transistors (TFTs) as sensing devices for electronic nose applications is presented. The concept of an electronic nose is demonstrated by using multiple solution-processed organic devices integrated into a single testbed. This testbed is used to examine two different analytes and to observe different responses for each type of active material. These results indicate that organic devices have the capacity to be used in sensor arrays for electronic nose applications. Findings show that these organic TFT sensors have the aptitude for discrimination between analytes based on their functional group chemistry. Sensor parameters such as thickness and device area are also examined to determine their effect on the sensor response.