Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.

Oxide Semiconductor Thin‐Film Transistors: A Review of Recent Advances

Electron and ambipolar transport in organic field-effect transistors.

https://iopscience.iop.org/article/10.1088/1468-6996/11/4/044305/pdf

Present status of amorphous In–Ga–Zn–O thin-film transistors

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

A novel amorphous oxide applicable, for example, to an active layer of a TFT is provided. The amorphous oxide comprises microcrystals.

Amorphous oxide and field effect transistor

A thin-film device includes a first electrical insulator, an oxide-semiconductor film formed on the first electrical insulator, and a second electrical insulator formed on the oxide-semiconductor film, the oxide-semiconductor film defining an active layer. The oxide-semiconductor film is comprised of a first interface layer located at an interface with the first electrical insulating insulator, a second interface layer located at an interface with the second electrical insulator, and a bulk layer other than the first and second interface layers. A density of oxygen holes in at least one of the first and second interlayer layers is smaller than a density of oxygen holes in the bulk layer.

Thin-film device and method of fabricating the same

The transfer characteristics of amorphous InGaZnO4 thin-film transistors (a-IGZO TFTs) were measured at temperatures ranging from 298 to 523 K in order to analyze the behavior of the above-threshold (ON state) and subthreshold regions. For comparison, the transfer characteristics of a hydrogenated amorphous silicon TFT (a-Si:H TFT) were measured in the same temperature range. We developed a simple analytical model that relates the threshold voltage (Vt) decrease due to increasing temperature to the formation of point defects in a-IGZO. It is well known that the formation of point defects results in the generation of free carriers in oxide semiconductors. Incorporating the analytical model with the experimental transfer characteristics data taken at high temperatures over 423 K, we estimated the formation energy to be approximately 1.05 eV. The Vt decrease because of the generation of point defects is peculiar to a-IGZO TFTs, which is not observed in a-Si:H TFTs. The results for the ON-current activation energy suggested that the density of tail states for a-IGZO is much lower than that for a-Si:H.

https://iopscience.iop.org/article/10.1143/JJAP.48.011301/pdf

Temperature-Dependent Transfer Characteristics of Amorphous InGaZnO4 Thin-Film Transistors

We investigated the threshold voltage shifts (ΔVT) of inverted-staggered hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) induced by steady-state (dc) and pulsed (ac) gate bias-temperature-stress (BTS) conditions. Our study showed that, for an equivalent effective-stress-time, ΔVT has an apparent pulse-width dependence under negative BTS conditions–the narrower the pulse width, the smaller the ΔVT. This gate-bias pulse-width dependence is explained by an effective-carrier-concentration model, which relates ΔVT for negative pulsed gate-bias stress to the concentration of mobile carriers accumulated in the conduction channel along the a-Si:H/gate insulator interface. In addition, our investigation of the methodology of a-Si:H TFT electrical reliability evaluation indicates that, instead of steady-state BTS, pulsed BTS should be used to build the database needed to extrapolate ΔVT induced by a long-term display operation. Using these experimental results, we have shown that a-Si:H TFTs have a satisfactory electrical reliability for a long-term active-matrix liquid-crystal display (AMLCD) operation.

https://iopscience.iop.org/article/10.1143/JJAP.37.4704/pdf

Electrical instability of hydrogenated amorphous silicon thin-film transistors for active-matrix liquid-crystal displays

We discuss the ultraviolet (UV) photo-field effects in amorphous InGaZnO4 thin-film transistors (a-IGZO TFTs) compared with those in hydrogenated amorphous silicon (a-Si:H) TFTs. It is shown that the UV illumination induces a much more significant threshold voltage (Vt) decrease and OFF-current increase for the a-IGZO TFTs than for the a-Si:H TFTs. The significant Vt decrease is found to take several tens of min to return to the initial state after switching off the UV light. A qualitative model is introduced to explain the photoresponse unique to the a-IGZO TFTs.

https://iopscience.iop.org/article/10.1143/JJAP.48.010203/pdf

Comparison of Ultraviolet Photo-Field Effects between Hydrogenated Amorphous Silicon and Amorphous InGaZnO4 Thin-Film Transistors

We compare the mutual interactions between the top-and bottom-gate fields in a dual-gate structure for amorphous InGaZnO4 (a-IGZO) and hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs). We find that a-IGZO TFTs show more significant mutual interactions than a-Si:H TFTs. By using a wide variety of a-IGZO TFTs with varying thicknesses of a-IGZO and gate-insulator layers, we have investigated, on the basis of a conventional fully depleted n-channel silicon-on-insulator model, the mechanism behind parallel shifts in transfer characteristics caused by negative top-gate voltages. Experimental results, even for relatively thick (over 150 nm) a-IGZO layers, are in good agreement with the fully depleted model. This fact may be related to the nonexistence of hole accumulation in a-IGZO, which is an intrinsic property of oxide semiconductors. In contrast, for the a-Si:H TFTs, there is a considerable discrepancy between the experimental results and the model. This discrepancy probably results from the limited penetration of band bending into the a-Si:H layer, as well as from the hole accumulation at the top interface. Such analysis of a-IGZO TFTs is of practical importance in device applications because many issues related to the fabrication and structure of a-IGZO TFTs may be resolved with a better understanding of dual-gate performance.

Dual-Gate Characteristics of Amorphous $ \hbox{InGaZnO}_{4}$ Thin-Film Transistors as Compared to Those of Hydrogenated Amorphous Silicon Thin-Film Transistors

Kazushige Takechi

Papers

Thin-film device and method of fabricating the same

Temperature-Dependent Transfer Characteristics of Amorphous InGaZnO4 Thin-Film Transistors

Electrical instability of hydrogenated amorphous silicon thin-film transistors for active-matrix liquid-crystal displays

Comparison of Ultraviolet Photo-Field Effects between Hydrogenated Amorphous Silicon and Amorphous InGaZnO4 Thin-Film Transistors

Dual-Gate Characteristics of Amorphous $ \hbox{InGaZnO}_{4}$ Thin-Film Transistors as Compared to Those of Hydrogenated Amorphous Silicon Thin-Film Transistors