Tin Oxide Based P and N-Type Thin Film Transistors Developed by RF Sputtering

Degradation induced by dynamic drain stress in both n-type and p-type low-temperature polycrystalline silicon thin-film transistors (TFTs) is systematically investigated. A transition-time-dependent hot-carrier (HC) mechanism is attributed to be the dominant degradation mechanism even for stress amplitudes close to the operation condition. Previously proposed nonequilibrium-drain-junction degradation model is further elaborated by including time-dependent carrier emission/recombination process. Different from that of n-type TFTs, a two-stage degradation behavior is first observed in p-type TFTs. By considering the effect of electron trapping in the initial stage on the dynamic HC mechanism in the second stage, degradation of both n-type and p-type TFTs can be consistently understood within a unified model, which also explains the absence of the two-stage degradation in n-type TFTs. Finally, this paper is further extended to show that the unified model should also be applicable to HC degradation induced by dynamic gate stress.

Over the past decade, amorphous metal oxide semiconductors have attracted great interest as low-cost alternatives to thin film transistors (TFTs) due to their high electron mobility, high optical transparency, good environmental/thermal stability, and processing versatility. In contrast, realization of high performance transparent p-type oxide semiconductors remain intangible with urgent industrial demands. In this work, we report solution-processed inorganic p-type copper iodide (CuI) and oxide thin film transistors (TFTs). The spin coated CuI film showed high mobility over 2 cm2 V-1 s-1 by proper treatments such as optimization process condition and applying dopant. Transparent complementary inverters composed of p-type CuI and n-type indium gallium zinc oxide TFTs are demonstrated. We also introduce our recent results of perovskite transistors.

The development of p-type metal oxide thin-film transistors (TFTs) is far behind the n-type counterparts. Here, p-type CuAlO2 thin films were deposited by spin coating and annealed in nitrogen atmosphere at different temperature. The effect of post-annealing temperature on the microstructure, chemical compositions, morphology, and optical properties of the thin films was investigated systematically. The phase conversion from a mixture of CuAl2O4 and CuO to nanocrystalline CuAlO2 was achieved when annealing temperature was higher than 900 °C, as well as the transmittance, optical energy band gap, grain size, and surface roughness of the films increase with the increase of annealing temperature. Next, bottom-gate p-type TFTs with CuAlO2 channel layer were fabricated on SiO2/Si substrate. It was found that the TFT performance was strongly dependent on the physical properties and the chemical composition of channel layer. The optimized nanocrystalline CuAlO2 TFT exhibits a threshold voltage of − 1.3 V, a mobility of ~ 0.1 cm2 V−1 s−1, and a current on/off ratio of ~ 103. This report on solution-processed p-type CuAlO2 TFTs represents a significant progress towards low-cost complementary metal oxide semiconductor logic circuits.

Solution-processable fullerene derivatives for organic photovoltaics and n-type thin-film transistors

Highly sensitive and selective room-temperature NO2 gas-sensing characteristics of SnOX-based p-type thin-film transistor

In this study, the plasma oxidation effect in tin-oxide (SnOx) thin film was investigated. And on this basis, we fabricated n-type thin-film transistors (TFTs) using the SnOx thin film with the plasma oxidation by experiments. By adjusting the processing time of the oxygen plasma treatment (OPT), the optimized SnOx TFT device exhibited an extremely high field-effect mobility of 87.6 cm2 V−1 s−1, a desirable on-to-off current ratio of 1.9 × 104 and a threshold voltage of − 0.9 V. Furthermore, we investigated the origin of the performance enhancements in the n-type SnOx TFTs with the optimized OPT by introducing the density of states (DOS) modeling in TCAD simulation. The numerical simulation indicated that the attributes of donor-like Gaussian defect states (oxygen vacancies) were modified in overall DOS due to the plasma oxidation effect. These present results show that the SnOx TFT treated by oxygen plasma has great promise in the future high-performance flat panel display industries.

Metal-Oxide thin-film transistors (TFTs) present unique opportunities to develop robust, low-cost and transparent electronics that can mechanically endure on flexible and stretchable substrates over large area in an industry compatible technology. Analog to digital converters (ADC) are an essential part of the Internet-of-Everything, where a multitude of sensing applications are envisaged, such as temperature and pressure sensor tags on human skin. In this work, dual-gate InGaZnO TFTs (IGZO) are demonstrated to achieve a 6-bit successive approximation (SAR) C-2C ADC operated at a clock of up to 400Hz and a power dissipation of 52.2µW at a power supply of V dd =15V. The ADC achieves a differential nonlinearity (DNL) of 0.7LSB and an integral nonlinearity (INL) of 0.58 LSB using only n-type TFTs. A figure of merit (FoM) of 66.7nJ/c.s. is achieved from an ADC on flexible substrate.

Currently, thin film transistor (TFT) based on planar structure is widely used in the applications of display panels. However, when the device is scaling-down, new device structures or novel materials should be introduced. In this work, the low temperature polycrystalline silicon (LTPS) TFT with fin-like structure is investigated. On the basis of electrical measurements, the device features good switching characteristics with low operating voltages. However, the I d–V g sweeping result exhibits off-state leakage, which is known as the gate-induced drain leakage (GIDL) current. The GIDL current is increased with the drain bias and the temperature increasing. To observe the GIDL current degradations, different gate biases with negative bias stress and positive bias stress are applied. The results show different degradation behaviors. In addition, bias stresses with DC and AC methods are also applied to verify the device reliability. Both threshold voltage (V t) shift and sub-threshold swing (S.S.) are also extracted to verify the degradations of the device. Finally, the physical models are also proposed to illustrate the degradation behaviors of the LTPS device with a fin-like structure, which can be beneficial to future related development of LTPS-based devices.

The discovery of oxide electronics is of increasing importance today as one of the most promising new technologies and manufacturing processes for a variety of electronic and optoelectronic applications such as next-generation displays, batteries, solar cells, memory devices, and photodetectors[1]. The high potential use seen in oxide electronics is due primarily to their high carrier mobilities and their ability to be fabricated at low temperatures[2]. However, since the majority of oxide semiconductors are n-type oxides, current applications are limited to unipolar devices, eventually developing oxide-based bipolar devices such as p-n diodes and complementary metal-oxide semiconductors.We have contributed to a wide range of oxide semiconductors and their electronics and optoelectronic device applications. Particularly, we have demonstrated n-type oxide-based thin film transistors (TFT), integrating In2O3-based n-type oxide semiconductors from binary cation materials to ternary cation species including InZnO, InGaZnO (IGZO), and InAlZnO. We have suggested channel/metallization contact strategies to achieve stable and high TFT performance[3, 4], identified vacancy-based native defect doping mechanisms[5], suggested interfacial buffer layers to promote charge injection capability[6], and established the role of third cation species on the carrier generation and carrier transport[7]. More recently, we have reported facile manufacturing of p-type SnOx through reactive magnetron sputtering from a Sn metal target[8]. The fabricated p-SnOx was found to be devoid of metallic phase of Sn from x-ray photoelectron spectroscopy and demonstrated stable performance in a fully oxide-based p-n heterojunction together with n-InGaZnO. The oxide-based p-n junctions exhibited a high rectification ratio greater than 103 at ±3 V, a low saturation current of ~2x10-10, and a small turn-on voltage of -0.5 V.In this presentation, we review recent achievements and still remaining issues in transition metal oxide semiconductors and their device applications, in particular, bipolar applications including p-n heterostructures and complementary metal-oxide-semiconductor devices as well as single polarity devices such as TFTs and memristors. In addition, the fundamental mechanisms of carrier transport behaviors and doping mechanisms that govern the performance of these oxide-based devices will also be discussed.ACKNOWLEDGMENTThis work was supported by the U.S. National Science Foundation (NSF) Award No. ECCS-1931088. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 20011028) by KRISS. K.N. was supported by Basic Science Research Program (NRF-2021R11A1A01051246) through the NRF Korea funded by the Ministry of Education.REFERENCES[1] K. Nomura et al., Nature, vol. 432, no. 7016, pp. 488-492, Nov 25 2004.[2] D. C. Paine et al., Thin Solid Films, vol. 516, no. 17, pp. 5894-5898, Jul 1 2008.[3] S. Lee et al., Journal of Applied Physics, vol. 109, no. 6, p. 063702, Mar 15 2011, Art. no. 063702.[4] S. Lee et al., Applied Physics Letters, vol. 104, no. 25, p. 252103, 2014.[5] S. Lee et al., Applied Physics Letters, vol. 102, no. 5, p. 052101, Feb 4 2013, Art. no. 052101.[6] M. Liu et al., ACS Applied Electronic Materials, vol. 3, no. 6, pp. 2703-2711, 2021/06/22 2021.[7] A. Reed et al., Journal of Materials Chemistry C, 10.1039/D0TC02655G vol. 8, no. 39, pp. 13798-13810, 2020.[8] D. H. Lee et al., ACS Applied Materials & Interfaces, vol. 13, no. 46, pp. 55676-55686, 2021/11/24 2021.

An investigation of drain pulse induced hot carrier degradation in n-type low temperature polycrystalline silicon thin film transistors

A highly efficient and stable electron injection layer (EIL) for inverted organic light-emitting diodes (OLEDs) is developed. A 1 nm-thick Al is deposited between indium tin oxide cathode and commonly used Cs2CO3 EIL, which can significantly improve the stability. The Al may react with evaporated Cs2CO3 and form a much stabler Al-O-Cs complex, avoiding Cs oxidization by air according to X-ray photoemission spectroscopy measurement. When the Al is evaporated after Cs2CO3 layer, although such a Al-O-Cs complex also forms, the inferior electron injection at Al/4,7-diphenyl-1,10-phenanthroline interface leads to a joule heat-induced resistance that adversely affects the air stability of the device. It is expected that the developed Al/Cs2CO3 EIL promotes high efficiency and stable active-matrix OLEDs based on n-type thin film transistor.

n and p-type nanocrystalline thin film transistors in coplanar top gate configuration have been processed at low temperature. All silicon layers (intrinsic, n and p-type) have been deposited by hot-wire chemical vapor deposition on glass substrates covered with SiO/sub 2/. Gate insulation has been achieved by means of high quality sputtered SiO/sub 2/. The maximum temperature reached during the whole process was 200/spl deg/C. Very high field effect mobility has been obtained for both kinds of devices, with values of 22 cm V/sup -1/s/sup -1/ for the electron mobility and around 1.0 cm V/sup -1/s/sup -1/ for the hole mobility.

In recent advancements, X-ray detectors have made significant progress. Active pixel sensors exhibit superior Signal-to-Noise Ratio (SNR) compared to passive counterparts. The conventional pixel circuit for X-ray detectors has three transistors and one capacitor. We focused on simplifying this pixel to enhance resolution. Our research introduces and verifies a novel pixel circuit developed for high-resolution X-ray detectors. The proposed pixel circuit is composed by two n-type thin-film transistors and one capacitor. It requires two scan pulses and three operational stages. This structure can effectively reduce the component area of the pixel circuit. We designed RPI LEVEL = 35 amorphous TFT model and simulated for verify our proposed pixel circuit. In results, proposed pixel circuit successfully operated and shows 2.5 μV when the equivalent resistance of detector (RDetector) is 10 MΩ, and 8.38 V when RDetector is 1 MΩ. To minimize the harmful effects of X-ray exposure, reducing the dosage is essential. Sensitivity and low noise are crucial factors, and the proposed circuit offers a compact design, increased sensitivity, and higher output voltage.

Air-stable n-doping of carbon nanotubes is presented by utilizing SiN(x) thin films deposited by plasma-enhanced chemical vapor deposition. The fixed positive charges in SiN(x), arising from (+)Si ≡ N3 dangling bonds induce strong field-effect doping of underlying nanotubes. Specifically, an electron doping density of ∼ 10(20) cm(-3) is estimated from capacitance voltage measurements of the fixed charge within the SiN(x). This high doping concentration results in thinning of the Schottky barrier widths at the nanotube/metal contacts, thus allowing for efficient injection of electrons by tunnelling. As a proof-of-concept, n-type thin-film transistors using random networks of semiconductor-enriched nanotubes are presented with an electron mobility of ∼ 10 cm(2)/V s, which is comparable to the hole mobility of as-made p-type devices. The devices are highly stable without any noticeable change in the electrical properties upon exposure to ambient air for 30 days. Furthermore, the devices exhibit high uniformity over large areas, which is an important requirement for use in practical applications. The work presents a robust approach for physicochemical doping of carbon nanotubes by relying on field-effect rather than a charge transfer mechanism.

Thin films of the semiconductor copper indium diselenide (CuInSe2) have been prepared at low temperature from a soluble precursor and incorporated into the first p-type thin-film transistors (TFTs) with spin-cast all-inorganic channels.