Multi-Segment TFT Compact Model for THz Applications

Abstract

We present an update of the Rensselaer Polytechnic Institute (RPI) thin-film transistor (TFT) compact model. The updated model implemented in Simulation Program with Integrated Circuit Emphasis (SPICE) accounts for the gate voltage-dependent channel layer thickness, enables the accurate description of the direct current (DC) characteristics, and uses channel segmentation to allow for terahertz (THz) frequency simulations. The model introduces two subthreshold ideality factors to describe the control of the gate voltage on the channel layer and its effect on the drain-to-source current and the channel capacitance. The calculated field distribution in the channel is used to evaluate the channel segment parameters including the segment impedance, kinetic inductance, and gate-to-segment capacitances. Our approach reproduces the conventional RPI TFT model at low frequencies, fits the measured current–voltage characteristics with sufficient accuracy, and extends the RPI TFT model applications into the THz frequency range. Our calculations show that a single TFT or complementary TFTs could efficiently detect the sub-terahertz and terahertz radiation.

Editors’ Choice—Thin Film Transistor Response in the THz Range

“…[32][33][34][35][36][37] An improved compact model based on the RPI TFT model and using the unified charge control model (UCCM) accounted for a non-exponential slope in the subthreshold regime by introducing a varying subthreshold slope and a non-trivial capacitance dependence on the gate bias. 31 These new features allowed us to obtain an excellent agreement with the measured I-V/C-V characteristics for both long and short n-channel and p-channel TFTs. The application of this new TFT model to the analysis of the TFT response required accounting for non-local potential distribution in the device channel.…”

“…Figure 2 shows the equivalent circuit of the multi-segment SPICE model for TFT and the equivalent circuit for each segment including leakage components. 31 The Drude inductances included in the SPICE model (…”

“…The improved TFT compact model used in this work is the extension of the TFT SPICE UCCM model described in references. 31,37 and implemented in Verilog-A. The improvement compared with the previous version 31 is a more accurate approximation for parameter λ e describing the output conductance.…”

“…Figure2. Equivalent circuit of the multi-segment SPICE model for TFT (a)31 and equivalent circuit for each segment including leakage components (b) 33. …”

“…Comparison of the simulated I-Vs for the one-segment SPICE model (lines) and the multi-segment SPICE model (circles) with the measured data (triangles) for the 0.8 μm n-channel TFT: (a) output characteristics and (b) transfer characteristics. The dashed lines in (b) illustrate the parameter extraction for the two subthreshold slopes 31.…”