Yoshinari Kimura

Threshold voltage control in dinaphthothienothiophene-based organic transistors by plasma treatment: Toward their application to logic circuits

The threshold voltage in p-channel organic thin-film transistors (TFTs) having dinaphthothienothiophene as a channel material has been investigated toward their applicability to logic circuits. Oxygen plasma treatment of the gate dielectric surface was carried out to control the threshold voltage. The threshold voltage changed in the range from −6.4 to 9.4 V, depending on plasma treatment time and the thickness of the gate dielectric. The surface charge after plasma treatment was estimated from the dependence of the threshold voltage. Operation of logic inverters consisting of TFTs with different threshold voltages was demonstrated as an application of TFTs with controlled threshold voltage.

Operational stability in pentacene thin-film transistors with threshold voltages tuned by oxygen plasma treatment

Pentacene-based organic thin-film transistors (TFTs) having a SiO2 gate dielectric treated with oxygen plasma have been investigated for control of the threshold voltage. The threshold voltage changed in the wide range from −15 to 80 V, depending on plasma treatment time, AC power for plasma generation, and gate dielectric thickness. The threshold voltage change was attributed to negative charges induced on and/or near the surface of the gate dielectric. The threshold voltage change on the order of 1 V was particularly proportional to plasma treatment time. The predictable change enables the control of threshold voltage in this range. In addition, the effect of gate bias stress on threshold voltage was examined. The results suggested that gate bias stress does not negate the threshold voltage change induced by plasma treatment.

Application of pentacene thin-film transistors with controlled threshold voltages to enhancement/depletion inverters

Oxygen plasma treatment has been carried out to control the threshold voltage in organic thin-film transistors (TFTs) having a SiO2 gate dielectric prepared by rf sputtering. The threshold voltage linearly changed in the range of −3.7 to 3.1 V with the increase in plasma treatment time. Although the amount of change is smaller than that for organic TFTs having thermally grown SiO2, the tendency of the change was similar to that for thermally grown SiO2. To realize different plasma treatment times on the same substrate, a certain region on the SiO2 surface was selected using a shadow mask, and was treated with oxygen plasma. Using the process, organic TFTs with negative threshold voltages and those with positive threshold voltages were fabricated on the same substrate. As a result, enhancement/depletion inverters consisting of the organic TFTs operated at supply voltages of 5 to 15 V.

Pentacene Thin-Film Transistors with Controlled Threshold Voltages and Their Application to Pseudo CMOS Inverters

Threshold voltage control in pentacene thin-film transistors (TFTs) has been demonstrated by oxygen plasma treatment to the surface of the SiO2 gate dielectric. The threshold voltage linearly shifts with increase in plasma treatment time. Pseudo CMOS inverters consisting of the TFTs with controlled threshold voltages successfully operated at 10 V.