Self-biased silicon transistor with a piezoelectric gate for an efficient mechanical energy harvesting device

In this study, a piezo potential gated self-biased transistor was fabricated on a heavily doped silicon (p⁺-Si) (111) substrate and used for efficient mechanical energy harvesting applications. The drain and source (S-D) electrode of this top gated transistor was made of LiF(5 nm)/Al(65 nm) and MoO₃(5 nm)/Ag(65 nm), respectively, whereas piezoelectric poly (vinylidene fluoride-<i>co</i>-hexapropelene) (PVDF-HFP) thin film was used as the gate dielectric. Drain bias (<i>V</i>_DS), which was required to transport the hole carrier through the channel, was developed from the work function difference of the S-D electrodes, whereas the piezopotential, which worked as the gate bias of this transistor, was developed from the external force applied on the PVDF-HFP thin film. Consequently, this device efficiently converted mechanical energy into electrical energy. For an applied pressure of 4 bar for ∼5 s, the extracted electrical power per cycle of this device was 1.6 × 10^-9 watts with a conversion efficiency of ∼75%, which was an exceptionally high value compared with conventional energy harvesting devices. Besides, the electrical characterization showed its transistor-like behavior, and the extracted device parameters, including threshold force, on-off ratio, and subthreshold swing (SS), were 0.5 N, 4.56 × 10², and 3.16 N A^-1, respectively.