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

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 low-temperature, solution-based preparation of amorphous, metal oxide semiconducting thin-films is reported. This ‘sol–gel on chip’ hydrolysis approach yields thin-film transistors with high field-effect mobilities, reproducible and stable turn-on voltages and high operational stability.

Low-temperature, high-performance solution-processed metal oxide thin-film transistors formed by a ‘sol–gel on chip’ process

Review of recent developments in amorphous oxide semiconductor thin-film transistor devices

The experimental and modeling study of bias-stress-induced threshold voltage instabilities in amorphous indium-gallium-zinc oxide thin film transistors is reported. Positive stress results in a positive shift in the threshold voltage, while the transfer curve hardly moves when negative stress is induced. The time evolution of threshold voltage is described by the stretched-exponential equation, and the shift is attributed to the electron injection from the channel into interface/dielectric traps. The stress amplitudes and stress temperatures are considered as important factors in threshold voltage instabilities, and the stretched-exponential equation is well fitted in various bias temperature stress conditions.

Bias-stress-induced stretched-exponential time dependence of threshold voltage shift in InGaZnO thin film transistors

We have investigated the static and dynamic bias stress-induced charge trapping and detrapping phenomenon in amorphous indium–gallium–zinc oxide thin film transistors. It is observed that the charges trapped after electron injection in the interface and bulk traps are unstable and slowly decay over time. The stretched-exponential equation, which can be derived based on the trapping/detrapping of charges to/from existing traps and continuous redistribution of charges in bulk dielectrics, is successfully applied in fitting the time dependence of the threshold voltage shift during the stress and recovery phases under dynamic stresses. The characteristic time constants decrease with increasing temperature and drain bias during the recovery phase. Under dynamic stresses with various frequencies, the threshold voltage shift strongly depends on the frequency of dynamic stresses, i.e., a high frequency stress results in a small threshold voltage shift and a long lifetime. The stress-induced threshold shift phenomenon is observed to be relieved after a long-time low temperature post thermal annealing process and device passivation with an aluminum oxide layer.

https://iopscience.iop.org/article/10.1088/0268-1242/24/1/015013/pdf

Charge trapping and detrapping characteristics in amorphous InGaZnO TFTs under static and dynamic stresses

A comparative study was made of the performance and electrical instabilities in amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors with Al2O3 and Al2O3/SiNx gate dielectrics Steeper subthreshold slope is observed in Al2O3 devices, which shows that the density of trap states at the interface of a-IGZO/Al2O3 is lower than that of a-IGZO/SiNx Under high bias-stresses, a larger degradation is observed in Al2O3/SiNx devices The device degradation for both devices are mainly attributed to the charge trapping phenomenon, but the different time dependence of threshold voltage shift shows that trapped electrons are more easily redistributed inside the Al2O3 dielectrics

Comparative Study of Electrical Instabilities in Top-Gate InGaZnO thin Film Transistors with Al2O3 and Al2O3/SiNx Gate Dielectrics

We have investigated the low-frequency noise (LFN) properties of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) as a function of frequency, bias, and channel length of devices. The measured noise power spectral density of drain current (S iD) shows that the low-frequency noise in a-IGZO TFTs obeys the classical 1/f noise theory, i.e., it fits well to a 1/f gamma power law with gamma ~ 1 in the frequency range of 10 Hz to 1 kHz. From the dependence of normalized noise power spectral density (S iD/ID 2) on the gate voltage, mobility fluctuation is considered as a dominant LFN mechanism in a-IGZO TFTs. The magnitude of S iD/ID 2 is inversely proportional to the channel length of devices, which indicates that contact noise is insignificant in a-IGZO TFTs.

Low-Frequency Noise in Amorphous Indium–Gallium–Zinc-Oxide Thin-Film Transistors

A high performance amorphous indium–gallium–zinc oxide (a-IGZO) thin film transistor (TFT) inverter is implemented using the enhancement mode driver and the depletion mode load. The threshold voltage of the TFT is easily controlled by adjusting the active layer thickness in a-IGZO TFTs. The proposed inverter shows much improved switching characteristics including higher voltage gain, wider swing range, and higher noise margins compared to the conventional inverter with an enhancement load.

https://iopscience.iop.org/article/10.1143/JJAP.48.100202/pdf

Jeong-Min Lee

Papers

Bias-stress-induced stretched-exponential time dependence of threshold voltage shift in InGaZnO thin film transistors

Charge trapping and detrapping characteristics in amorphous InGaZnO TFTs under static and dynamic stresses

Comparative Study of Electrical Instabilities in Top-Gate InGaZnO thin Film Transistors with Al2O3 and Al2O3/SiNx Gate Dielectrics

Low-Frequency Noise in Amorphous Indium–Gallium–Zinc-Oxide Thin-Film Transistors

Full-Swing InGaZnO Thin Film Transistor Inverter with Depletion Load