Low-power And High-performance Electronic Devices Based On Ultra-thin Indium-tin-oxide

Oxide semiconductors are well-known for wide-bandgap(E_g>2 e V),decent mobility(?_FE=10?100 cm²/V·s),and low-temperature fabrication(T<400?).They are often used as channel material in thin film transistors(TFTs).Over the recent years,a great deal of studies have demonstrated that the oxide semiconductors have strong immunity to the short-channel-effects and achieve high-performance field-effect transistors with extremely low static power consumption,which is appealing to ultralow-power electronics,and provides ideas for the development of the next generation semiconductor.Indium-tin-oxide(ITO)is a highly conductive,tin-doped semiconductor with a wide bandgap of around 3.5 e V and mobility of around 30 cm²/V·s.Indium-tin-oxide is currently rarely used as an active channel material due to its unsatisfactory switching performance.However,as a transparent conducting oxide,it is the material most widely used in coatings,solar cells and,most importantly,the display industry.Such a well-developed material with industry-wide availability has very intriguing electronic properties that are desirable as an active channel material,in both TFTs and high-performance electronic transistors.In addition,the relative dielectric constant of indium-tin-oxide is lower than that of indium-gallium-zinc-oxide(IGZO)or zinc-oxide(Zn O),which enable indium-tin-oxide to realize ultra-short channel devices with low power consumption.Thus,we conducted a comprehensive study on material properties of indium-tin-oxide.Benefited from ultrathin device structure and perfect interface quality,we successfully fabricated high-performance and low-power electronics based on indium-tin-oxide.At first,we adjusted the oxygen partial pressure in the sputtering process of indium-tion-oxide and decreased the film thickness.As a consequence,we compensated the oxygen vacancy in the film and transformed the indium-tin-oxide from the metallic state to the semiconducting state.Secondly,we chose high?material of lanthanum-doped hafnium oxide(Hf La O)as gate dielectric and realized fully-depleted transistors.Thirdly,we adopted ultrathin body with 3.5-nm-thick indium-tin-oxide and 5-nm-thick Hf La O to realize ultra-short-channel devices.The 15-nm-long device exhibited ultralow off-state current lower than 10 f A/?m and ultrahigh on/off ratio up to 10¹¹.It showed good immunity to short-channel-effects and demonstrated the great potential of indium-tin-oxide in the low-power electronics.Based on the excellent subthreshold and saturation characteristics of indium-tin-oxide transistors,we designed an enhancement-depletion mode(E-D)inverter with ultrahigh gain.At a bias of 2.5 V,the inverter gain was up to 467,which was by far the record-high value in oxide-semiconductor-based inverters,and also far superior to inverters based on two-dimensional materials,such as molybdenum disulfide(Mo S₂)and black phosphorous(BP).Then,we used these ultrahigh-gain inverters to construct three basic circuit units,the NAND gate,the NOR gate,and the SRAM,and all achieved stable logic output performance.Finally,we designed a bootstrapped(BST)inverter derived from the enhancement-enhancement mode(E-E)inverter,and fabricated a five-stage ring oscillator with propagation delay of 0.49 ns/stage,which was the best value among oxide-semiconductor-based ring oscillators,and thus verified the extremely high operating speed of indium-tin-oxide transistors.We fabricated radio-frequency(RF)transistors based on indium-tin-oxide,and achieved simultaneously the cut-off frequency of f _T and the maximum oscillation frequency f_max above 10 GHz,which was superior to the same type of RF transistors.We carried analysis of mixer characteristics on the indium-tin-oxide transistors and further confirmed the indium-tin-oxide potential in the field of high performance electronic devices.The study on indium-tin-oxide transistors has not only tremendously expanded the research on metal-oxide semiconductors,but also provided a new direction for the development of the next generation semiconductor.