Enhanced performance of room temperature ammonia sensors using morphology-controlled organic field-effect transistors

Review of recent advances and sensing mechanisms in solid-state organic thin-film transistor (OTFT) sensors

“…79 Unni and coworkers demonstrated enhanced performance of room temperature NH 3 sensors by controlling the thickness and growth dynamics of the organic semiconductor dinaphtho [2,3- b :2′,3′- f ]thieno[3,2- b ]thiophene (DNTT) at thicknesses from 5 nm, resulting in a film with discrete crystallites, 12 nm, resulting in a nano-crystalline porous film and 50 nm, resulting in a continuous polycrystalline film. 42 The DNTT film having a nano-crystalline porous morphology resulting from a thinner film demonstrated a two-fold increase compared to the device with a continuous layer at 1 ppm NH 3 with the optimized sensor demonstrating a sensitivity of 17.5% at 100 ppb and a response/recovery time of 1 min/2 min. Wang and coworkers reported the thickness optimization of thermally evaporated VOPc-based OTFT sensors which were grown on a para -sexiphenyl ( p -6P) templating layer to enhance the crystallinity of the semiconductor to develop humidity and NH 3 sensors (Fig.…”

“…Among strong redox gases, the quantification of NH 3 , H 2 S, NO/NO 2 and SO 2 are particularly useful since they are industrially produced chemicals or pollutants generated as a result of manufacturing processes or emitted in automobile combustion engines. 36,37 A number of organic semiconductors incorporated into OTFTs have been reported to be sensitive to NH 3 , [38][39][40][41][42][43][44] H 2 S, [45][46][47][48] NO 2 , [49][50][51][52][53][54][55] and SO 2 . 56 OTFT redox gas sensors often offer advantages over metal-oxide-based sensors owing to their less strict operational requirements.…”

“…Porous OTFTs. Since RR, S and t 90 can be enhanced by improving analyte diffusion and increasing the specific surface area of the semiconductor in OTFTs, 151 the fabrication of porous films with controlled morphologies rather than those naturally arising from previously-discussed deposition conditions 42 is one pathway being explored for next-generation OTFT sensors. One commonly reported technique for the formation of porous, thin-film semiconductors is using a template for controlled pore formation, where the dispersity of pore sizes in the film is narrow, since pore size has been demonstrated to have a direct influence on RR.…”

“…The effect of increasing NH 3 concentration on the I on / I off ratio is stronger in devices where the semiconductor layer was less thick, enabling easier diffusion of the analyte to the dielectric–semiconductor interface. 42 The rate of diffusion through the bulk of the film, as well as the rate of absorption and desorption of gases to the semiconductor–dielectric interface also affect sensor response as demonstrated by Chi and coworkers who fabricated OTFT sensors with a spirobifluorene-based polymer as the semiconductor with thicknesses from 5 to 25 nm. 48 The magnitude of the sensor response increased as the active layer thickness decreased from 25 nm to 20 nm, followed by a decrease in the magnitude of the response as thickness further decreased to 15 nm and 5 nm, respectively.…”

Influence of Polymer Gate Dielectric on Organic Field‐Effect Transistors: Interdependence of Molecular Weight, Solvent Polarity, and Surface Energy—A Case Study with PMMA and Pentacene

“…Good thermal and mechanical stability together with a high electrical resistivity (>2 × 10 15 ohm.cm) and a dielectric constant similar to that of silicon dioxide make PMMA a good candidate to be used as gate dielectric in OFETs. [15][16][17][18][19][20] It is also understood that the performance of a polymeric gate dielectric is defined by an interplay of its surface energy, morphology, capacitance, and leakage current. These physical properties in turn depend on the molecular weight and the solvent chosen for the polymer processing.…”