ZnO is an attractive material for applications in electronics, photonics, acoustics, and sensing In optical emitters, its high exciton binding energy (60 meV) gives ZnO an edge over other semiconductors such as GaN if reproducible and reliable p-type doping in ZnO were to be achieved, which currently remains to be the main obstacle for realization of bipolar devices On the electronic side, ZnO holds some potential in transparent thin film transistors (TFTs) owing to its high optical transmittivity and high conductivity Among the other promising areas of application for ZnO are acoustic wave devices, due to large electromechanical coupling in ZnO, and devices utilizing nanowires/nanorods such as biosensors and gas sensors and solar cells, since it is relatively easy to produce such forms of ZnO nanostructures, which have good charge carrier transport properties and high crystalline quality Despite the significant progress made, there is still a number of important issues that need to be resolved before ZnO can be transitioned to commercial use, not to mention the stiff competition it is facing with GaN, which is much more mature in terms of devices In this paper, recent progress in device applications of ZnO is discussed and a review of critical issues for realization of ZnO-based devices is given

https://doc.rero.ch/record/21182/files/_zg_r_mit_-_ZnO_Devices_and_Applications_A_Review_of_Current_20101229.pdf

ZnO Devices and Applications: A Review of Current Status and Future Prospects

Over the past two decades, several advances have been made in micromachined sensors and actuators. As the field of microelectromechanical systems (MEMS) has advanced, a clear need for the integration of materials other than silicon and its compounds into micromachined transducers has emerged. Piezoelectric materials are high energy density materials that scale very favorably upon miniaturization and that has led to an ever-growing interest in piezoelectric films for MEMS applications. At this time, piezoelectric aluminum-nitride-based film bulk acoustic resonators (FBAR) have already been successfully commercialized. Future innovations and improvements in inertial sensors for navigation, high-frequency crystal oscillators and filters for wireless applications, microactuators for RF applications, chip-scale chemical analysis systems and countless other applications hinge upon the successful miniaturization of components and integration of piezoelectrics and metals into these systems. In this article, a comprehensive review of micromachined piezoelectric transducer technology will be presented. Piezoelectric materials in bulk and thin film forms will be reviewed and fabrication techniques for the integration of these materials for microsensor applications will be presented. Recent advances in various piezoelectric microsensors will be presented through specific examples. This review will conclude with a critical assessment of the future trends and promise of this technology.

https://iopscience.iop.org/article/10.1088/0957-0233/20/9/092001/pdf

Piezoelectric MEMS sensors: state-of-the-art and perspectives

The authors report on the fabrication of thin film transistors (TFTs), which use an amorphous indium gallium zinc oxide (a-IGZO) channel, by rf sputtering at room temperature and for which the channel length and width are patterned by photolithography and dry etching. To prevent plasma damage to the active channel, a 100-nm-thick SiOx layer deposited by plasma enhanced chemical vapor deposition was adopted as an etch stopper structure. The a-IGZO TFT (W∕L=10μm∕50μm) fabricated on glass exhibited a high field-effect mobility of 35.8cm2∕Vs, a subthreshold gate swing value of 0.59V∕decade, a thrseshold voltage of 5.9V, and an Ion∕off ratio of 4.9×106, which is acceptable for use as the switching transistor of an active-matrix TFT backplane.

High mobility bottom gate InGaZnO thin film transistors with SiOx etch stopper

Thin film transistors (TFTs) with oxide semiconductors have drawn great attention in the last few years, especially for large area electronic applications, such as high resolution active matrix liquid crystal displays (AMLCDs) and active matrix organic light-emitting diodes (AMOLEDs), because of their high electron mobility and spatial uniform property. This paper reviews and summarizes recent emerging reports that include potential applications, oxide semiconductor materials, and the impact of the fabrication process on electrical performance. We also address the stability behavior of such devices under bias/illumination stress and critical factors related to reliability, such as the gate insulator, the ambient and the device structure.

Review paper: Transparent amorphous oxide semiconductor thin film transistor

Films of the high-performance solution-processed amorphous oxide semiconductor a-ZnIn4Sn4O15, grown from 2-methoxyethanol/ethanolamine solutions, were used to fabricate thin-film transistors (TFTs) in combination with an organic self-assembled nanodielectric as the gate insulator. This structurally dense-packed semiconductor composition with minimal Zn2+ incorporation strongly suppresses transistor off-currents without significant mobility degradation, and affords field-effect electron mobilities of ∼90 cm2 V−1 s−1 (104 cm2 V−1 s−1 maximum obtained for patterned ZITO films), with Ion/Ioff ratio ∼105, a subthreshhold swing of ∼0.2 V/dec, and operating voltage <2 V for patterned devices with W/L = 50. The microstructural and electronic properties of ZITO semiconductor film compositions in the range Zn9−2xInxSnxO9+1.5x (x = 1−4) and ZnIn8−xSnxO13+0.5x (x = 1−7) were systematically investigated to elucidate those factors which yield optimum mobility, Ion/Ioff, and threshold voltage parameters. It is shown tha...

High-performance solution-processed amorphous zinc-indium-tin oxide thin-film transistors.

The authors report on transparent thin-film transistors using amorphous indium zinc oxides for an active channel layer and gate-source-drain electrodes fabricated by rf magnetron sputtering at room temperature. The conducting properties of the amorphous indium zinc oxides were controlled by oxygen partial pressures in the sputtering ambient. An amorphous AlOx served as the gate dielectric oxide. Devices were realized that display a threshold voltage of 1.1V and an on/off ratio of ∼106 operated as a n-type enhancement mode with saturation mobility of 0.53cm2∕Vs. The devices showed optical transmittance about 80% in the visible range.

Transparent amorphous indium zinc oxide thin-film transistors fabricated at room temperature

Indium-zinc oxide (IZO) films were grown on glass substrates by rf magnetron sputtering using targets of 50mol% In2O3–50mol% In2O3(ZnO)3 and In2ZnkOk+3 (k=3, 4, 5, and 7) at room temperature and 300°C. The difference in Zn content between the films and the sputter targets varied with the growth temperature. The structural, electrical, and optical properties of the IZO films were investigated as a function of Zn content. The crystal structure of IZO films grown at room temperature changed from amorphous to crystalline at a Zn content (Zn∕(Zn+In)) of 68at.%. IZO films grown at 300°C using a target of 50% In2O3–50% In2O3(ZnO)3 had a Zn content of 40at.% and its x-ray diffraction peaks were matched with those of ITO. As the Zn content in IZO thin films grown at 300°C increased from 40to74at.%, the conductivity and optical band gap energy decreased.

Effects of Zn content on structural and transparent conducting properties of indium-zinc oxide films grown by rf magnetron sputtering

Dry etching of zinc-oxide and indium-zinc-oxide in IBr and BI3 plasma chemistries

High-density plasma etching of indium–zinc oxide films in Ar/Cl2 and Ar/CH4/H2 chemistries

The etching characteristics of indium zinc oxide (IZO) films were investigated using a high-density plasma in Ar, Ar∕Cl2, and Ar∕CH4∕H2 chemistries. The IZO layers were deposited by means of rf magnetron sputtering, in which the target composition and growth temperature were varied to selectively tune the film properties. X-ray diffraction, elastic recoil detection, and Rutherford backscattering spectroscopy were used to determine the crystallization quality, atomic density, and composition of the as-deposited IZO films. As the In∕(In+Zn) composition ratio in the IZO layer increases, the etch yield in Ar and Ar∕Cl2 plasmas remains fairly constant, indicating that the etching dynamic is essentially independent of the film properties. In sharp contrast, a strong increase of the IZO etch yield with the In∕(In+Zn) fraction is observed in Ar∕CH4∕H2 plasma due to the preferential desorption of the group-III etch products. By comparing these experimental data to the predictions of a simple rate model accounting for preferential desorption effects, it is concluded that the balance between etching and polymer deposition in the Ar∕CH4∕H2 plasma plays an important role in the evolution of the IZO etch rate with the In concentration fraction.

Ju-Il Song

Papers

Transparent amorphous indium zinc oxide thin-film transistors fabricated at room temperature

Effects of Zn content on structural and transparent conducting properties of indium-zinc oxide films grown by rf magnetron sputtering

Dry etching of zinc-oxide and indium-zinc-oxide in IBr and BI3 plasma chemistries

High-density plasma etching of indium–zinc oxide films in Ar/Cl2 and Ar/CH4/H2 chemistries

Influence of the film properties on the plasma etching dynamics of rf-sputtered indium zinc oxide layers