Low-Operating-Voltage Ultrathin Junctionless Poly-Si Thin-Film Transistor Technology for RF Applications

In this letter, for the first time, we experimentally investigate the radio-frequency (RF) characteristics and low-frequency noise (LFN) of n-type planar junctionless (JL) poly-Si thin-film transistors (TFTs). The fabricated JL devices show remarkable dc performance with good current drive and a high on-current/off-current ratio of 8 × 10⁷. Furthermore, with the implementation of an in situ phosphorus-doped channel architecture and a salicide process, the JL device with a channel length of 0.4 μm exhibits a cutoff frequency (f_t) of 3.36 GHz and a maximum oscillation frequency (f_max) around 7.37 GHz at a drain bias of 2 V. As far as LFN is concerned, the JL device shows approximately four orders of magnitude lower drain-current noise power spectral density (S_id) over conventional inversion-mode counterparts. These results demonstrate that the JL poly-Si TFT technique is promising for RF modules implemented in system-on-panel applications.