Metal-Semiconductor Field-Effect Transistor Made Using Amorphous In-Ga-Zn-O Channel and Bottom Pt Schottky Contact Structure at 200 C

Abstract

Amorphous In-Ga-Zn-O (a-IGZO) based metal-semiconductor field-effect transistors (MESFETs) were fabricated at 200 • C. A bottom Pt structure was employed to form a good Schottky gate, and channel thickness was optimized to 230 nm to obtain high on-currents I on > 10 −6 A, on-to-off current ratios > 10 6 and low subthreshold voltage swing of 129 mV/decade. The field-effect mobility (μ FE ) was as small as 0.5 cm 2 (Vs) −1 , which is explained quantitatively by the subgap trap density in the 200 • C-annealed a-IGZO. The present result suggests that a double-layered channel with different donor densities will be effective to improve I on and μ FE of a-IGZO MESFETs.Amorphous oxide semiconductors (AOSs) represented by amorphous In-Ga-Zn-O (a-IGZO) have attracted much attention since the first report of flexible and transparent thin-film transistors (TFTs) fabricated at room temperature (RT). 1,2 AOS TFTs have superior properties such as high field-effect mobilities (μ FE ) >10 cm 2 (Vs) −1 , low operation voltages, 3 and low-temperature processes. Therefore, they are considered to be most promising to develop future flexible devices as demonstrated by several prototype displays and integrated circuits. 4,5 To date, most of AOS TFTs have employed metal-insulatorsemiconductor field-effect transistor (MISFET) structures, and various gate dielectric materials (e.g. SiO 2 , SiN x , SiON x , Y 2 O 3 , Al 2 O 3 , (Ba,Sr)TiO 3 , and organics) have been examined. 1,6-11 For the MISFET structures, it is crucial to choose a suitable gate insulator material and a preparation method in order to minimize degradation of TFT performances. The quality of the gate insulator and the insulator-channel interface is evaluated from the subthreshold voltage swing (S) because it is related to the subgap trap density D sg by (k B T/e)ln 10 (1 + D sg /C G ) (C G is the gate capacitance). Therefore, it is important to form a high-quality insulator layer and an interface with low D sg but this is still a challenging issue in particular for flexible devices that require low process temperatures e.g. < 200 • C.On the other hand, a metal-semiconductor FET (MESFET) using a Schottky gate contact requires no insulator layer and can be fabricated by a simpler and less expensive process; therefore, MESFET has been employed e.g. for GaAs that cannot form a good gate insulator. However, MESFET has some restrictions; e.g., (i) a good Schottky contact must be formed, and (ii) an applicable V GS is limited by the built-in potential (V bi ) of the Schottky contact. The former is a serious issue for oxide semiconductors because it is difficult to form stable and good Schottky junctions with oxide semiconductors including crystalline ZnO and AOSs due to their sensitivity to methods and conditions to prepare the metal-oxide semiconductor interface. 12,13 Consequently, for AOS-based FETs, only one paper on MESFET has been reported to date. 14 We previously reported fabrication of a nearly ideal a-IGZO/Pt Schottky diode by employing a bottom Pt structure. 15 In thi...

In–Ga–Zn–O MESFET with transparent amorphous Ru–Si–O Schottky barrier

“…(1) equals 7.36 cm 2 /V s. This confirms that the MESFET channel mobility equals the bulk mobility of the respective semiconductor. The subthreshold swing obtained from slope of transfer characteristic was SS = 420 mV/dec and is in the range reported for IGZO thin‐film transistors 6, 9.…”

“…Up to date only few research groups have presented IGZO MESFET devices. Lee et al used Pt as gate electrode in IGZO MESFET exhibiting subthreshold swing (SS) parameter value of 129 mV/dec, I ON / I OFF ratio on the level of 10 6 A/A, and channel mobility as small as 0.5 cm 2 /V s, explained by the subgap trap density in the 200 °C annealed a‐IGZO 9. Lorenz et al utilized Ag x O as gate electrode in order to fabricate MESFETs with a‐IGZO layer annealed at temperature of 150 °C, presenting SS of 112 mV/dec, I ON / I OFF ratio on the level of 2.5 × 10 7 A/A, and channel mobility as high as 15 cm 2 /V s 6.…”

Interfacial Chemistry-Induced Modulation of Schottky Barrier Heights: In Situ Measurements of the Pt–Amorphous Indium Gallium Zinc Oxide Interface Using X-ray Photoelectron Spectroscopy

“…There is increasing interest in using transparent amorphous oxide semiconductors (TAOS) for ubiquitous electronic devices due to their excellent electronic performance and their potential for novel transparent electronics. The most promising TAOS material to date is amorphous-indium gallium zinc oxide (a-IGZO), which is currently used as an active material for thin-film transistors (TFTs) in active matrix displays. , Other applications for a-IGZO include photodetectors, Schottky − and pn diodes, metal–semiconductor field-effect transistors, , Schottky-barrier TFTs, strain gauges, chemical and biological sensors, resistive random access memory (RRAM), , and memristors . A benefit of a-IGZO is that there is a fairly high degree of flexibility on the range of In/Ga/Zn ratios used for the active semiconductor in a TFT or as a switching layer in RRAM .…”

Quantum Confinement Effect in Amorphous In–Ga–Zn–O Heterojunction Channels for Thin-Film Transistors

“…Carrier density (n e ) of the IGZO-111 was set at~1 × 10 17 cm −3 to obtain good Schottky contact, while that of the IGZO-high-In was set at~3 × 10 18 cm −3 to enhance the difference of N bg at the heterojunction interface. The N bg was estimated using an equation as shown below [34,35];…”