Acoustically improved performance in poly(3-hexylthiophene) based organic field effect transistor

Abstract

Demonstration of acoustically improving charge transport characteristics of regioregular poly(3-hexylthiophene) (rrP3HT) based organic field effect transistor (OFET) fabricated on YZ lithium niobate piezoelectric substrate has been presented and analyzed. Owing to the acoustoelectric (AE) effect, a surface acoustic wave (SAW) propagating through the substrate transfers its momentum and energy to the charges in the rrP3HT channel, reducing the effective energy gap between the charge hopping states, which leads to a decrease in charge trapping and an increase in path conductivity and number of paths for charge transport. Hence, a significant increase in drain current and mobility and a substantial reduction in gate voltage were observed in the presence of SAW. The AE effect has been especially predominant in devices with smaller channel width, depicting that gate voltage brought down by 30 V provided drain current equivalent to that obtained in the absence of SAW. The bias stress analysis of the devices showed an increase in current instead of the decrease, generally seen with respect to time, reinforcing that the long term charge trapping effect in OFETs can be compensated with the propagation of SAW leading to enhanced device stability.

Acoustic interactions with semiconductors: progression from inorganic to organic material system

“…The crucial factor of device stability with repeated exposure to SAW was also attained. The influence of the AE effect on the properties of rrP3HT-based OFETs showed acoustically improved performance parameters, such as a significant increase in the drain current and mobility, and a substantial reduction in the gate voltage, predominantly in devices with a smaller channel width [90]. In the presence of SAW, the gate voltage could be brought down by 20 V to 30 V in devices with a smaller channel width.…”

“…Generally, an OFET's operating condition requires a high applied voltage constrained by the high band gap and low relative permittivity of the gate dielectric material in use, and OFETs face stability problems over time due to the presence of trap states in the semiconducting channel and semiconductor-dielectric interface. As a consequence of the transfer of SAW momentum and energy to the charges in the direction of wave propagation [86], modulation of charge transport in an rrP3HT-based p-type OFET has also been achieved via the AE effect [90]. The implications of the AE effect on the performance of the OFET were studied with Rayleigh SAW devices fabricated on a piezoelectric substrate, YZ LiNbO 3 , and figure 13 shows the structure of the bottom gate top contact (BGTC) OFET.…”

“…Remarkably, in a bias stress study done on the OFET, the most prominent effect reported with acoustic wave propagation was the gradual increase in I DS until a surplus of 4.4% in ∼3700 s and embarking on a constant current afterward, as shown in figure 15. The added enhancement in the final current was attributed to the amount of charge de-trapped from deep traps present in the rrP3HT as well as the dielectric polymethyl methacrylate (PMMA) layer at room temperature [90,91]. The importance of acoustic interaction was brought to light with mitigation of the stability issue in the OFET under test.…”

“…Figure 13. Device setup of a fabricated rrP3HT-based OFET structure with BGTC configuration on a YZ LiNbO 3 substrate.Reprinted from[90], with the permission of AIP Publishing.…”