Depletion-mode Thin-film Transistors Research Articles

Transparent Transistors Based on Semiconducting Oxides

ABSTRACTThe synthesis and properties of oxide-based thin film transistors (TFTs) is reported using pulsed laser deposition. The field effect transistors use ZnO as the channel material. Low leakage current density is achieved with amorphous (CeTb)MgAl11O19 (CTMA) serving as the gate oxide, whose dielectric strength is measured to be > 5MV/cm for structures fabricated on Indium Tin oxide (ITO) substrates. Capacitance-voltage properties show that n-type active layers are realized with undoped ZnO. Charge densities in undoped ZnO are measured to be 1018 to 1019 / cm3 using Hall measurement and CV plots. Current-voltage measurements for TFT operation are reported. Channel materials on patterned substrates show high conductance and modulation of channel conductance. C-V measurements with MOS structure using doped ZnO and ZnxMg1-xO will also be described. The properties of depletion mode TFTs fabricated with doped and undoped oxide channel will be discussed in detail.

Junction devices based on sulfonated polyaniline

Schottky diodes were fabricated using aluminum/neutralized-sulfonated-polyaniline (SPAN) junctions. I–V and C–V measurements were made, and the barrier height (ΦB) and the background concentration (NB) were determined to be 0.8 V and 4×1017/cm3, respectively. Using these diodes as gate control, depletion-mode thin-film transistors were fabricated with a source and drain made of gold Ohmic contacts. The transistors were characterized by I–V measurements, and the carrier mobility determined from devices operating in the |VG|>|VDS| “linear” regime was about 0.01 cm2/V s. This high value of mobility could be attributed to the spherulitic (partially ordered) structures observed in the SPAN thin films. Field-effect transistors were also fabricated on SPAN films deposited on an n-doped silicon substrate acting as the gate electrode with a thermally grown oxide layer. A reasonably high on/off ratio (∼4×103) was measured in these devices.

High-performance a-Si:H thin-film transistor using lightly doped channel

The fabrication of amorphous silicon thin-film transistors (TFTs) using a lightly phosphorus-doped channel is discussed. The transistors achieve an on-off current ratio exceeding six orders of magnitude and a field effect mobility of 0.4 cm/sup 2//V-s. These characteristics are found to be much better than those using an undoped channel with the same device structure. It is found that the incorporation of phosphorus in the channel can compensate the interface states and improve the transconductance of the TFT. It is shown that the fabrication of a depletion-mode TFT is fully compatible with the conventional enhancement-mode TFT process.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thin-film transistor useful for linear integrated circuits

A depletion-mode thin-film transistor is presented in which magnesium fluoride is used as the insulating layer material. The proposed application for linear integrated circuits is based upon the suitably large drain current under no-gate bias and the good linearity of the amplification characteristics.