Enhanced capacitance ratio and low minimum capacitance of varactor devices based on depletion-mode Ga-doped ZnO TFTs with a drain-offset structure

Abstract

Depletion-mode Ga-doped ZnO thin-film transistors (TFTs) with a drain-offset configuration were fabricated employing a plasma-enhanced chemical vapour deposited Si 3 N 4 gate insulator and a metal organic chemical vapour deposition grown Ga-doped ZnO channel layer. For comparison, conventional TFTs with drain-to-gate overlap were also fabricated. Capacitance-voltage characteristics of gate-to-drain capacitors and current-voltage characteristics of TFTs were measured. Although drain-offset TFTs exhibit poor device characteristics compared with conventional TFTs, these TFTs show better C max /C min ratio and C min values. The C max /C min ratio is as large as 71.83 and C min is as small as 0.3 fF µm −1 normalized for channel width, demonstrating the potential of these devices as varactors for circuit applications. Their better varactor performance is ascribed to the presence of a very small capacitance in the drain-offset region. The effect of drain-offset length variation on TFT and gate-to-drain capacitor performance is also reported.

Low-frequency noise in high performance and stability of Li-doped ZnO thin-film transistors

“…Therefore, the metal cations such as Al, Li, In and Ga has been explored for creating doped ZnO TFTs with enhanced mobility and stability [15][16][17]. Among these cations, the Li is non-toxic and less expensive than In and Ga.…”

Investigations on the roles of position controlled Al layers incorporated into an Al-doped ZnO active channel during atomic layer deposition for thin film transistor applications

“…Generally, the stretched-out and positively-shifted C-V curves observed at higher frequency can result from the presence of traps in the active layer and=or at the interface between the active and gate insulator layers. 30) Because the interfacial properties were expected to be nearly the same for both devices, the trap centers located in the bulk region of the active channel caused significant effects on the deviations in C-V curves for the "focus" device at 1 MHz. A higher trap density for the "focus" device was also reflected as degradation in the SS value, as shown in Table I.…”

Reconfigurable-focus flat lens based on gradient index metamaterials

“…The varactor diode simulated in this paper may be realized by SMV2019 from Skyworks, which has a tuning range of 0.13-2.25 pF under the bias voltage of 20-0 V [39]. A varactor diode with a lower minimum capacitance may be realized by depletion-mode Ga-doped ZnO thin-film transisters with a drain-offset structure [40]. The hole width a and capacitance c of varactor diodes are identical in each hole array but vary in different hole arrays.…”