Revisiting the delta-phase of poly(vinylidene fluoride) for solution-processed ferroelectric thin films Li, Mengyuan; Wondergem, Harry J.; Spijkman, Mark-Jan; Asadi, Kamal; Katsouras, Ilias; Blom, Paul W. M.; de Leeuw, Dago M.

The first dual‐gate thin‐film transistor (DGTFT) was reported in 1981 with CdSe as the semiconductor. Other TFT technologies such as a‐Si:H and organic semiconductors have led to additional ways of making DGTFTs. DGTFTs contain a second gate dielectric with a second gate positioned opposite of the first gate. The main advantage is that the threshold voltage can be set as a function of the applied second gate bias. The shift depends on the ratio of the capacitances of the two gate dielectrics. Here we review the fast growing field of DGTFTs. We summarize the reported operational mechanisms, and the application in logic gates and integrated circuits. The second emerging application of DGTFTs is sensitivity enhancement of existing ion‐sensitive field‐effect transistors (ISFET). The reported sensing mechanism is discussed and an outlook is presented.

Buried electrodes and protection of the semiconductor with a thin passivation layer are used to yield dual‐gate organic transducers. The process technology is scaled up to 150‐mm wafers. The transducers are potentiometric sensors where the detection relies on measuring a shift in the threshold voltage caused by changes in the electrochemical potential at the second gate dielectric. Analytes can only be detected within the Debye screening length. The mechanism is assessed by pH measurements. The threshold voltage shift depends on pH as ΔVth = (Ctop/Cbottom) × 58 mV per pH unit, indicating that the sensitivity can be enhanced with respect to conventional ion‐sensitive field‐effect transistors (ISFETs) by adjusting the ratio of the top and bottom gate capacitances. Remaining challenges and opportunities are discussed.