We report the field-effect transistors using quasi-two-dimensional electron gas generated at an ultrathin (∼10 nm) AlO/TiO heterostructure interface grown via atomic layer deposition (ALD) on a SiO/Si substrate without using a single crystal substrate. The 2DEG at the AlO/TiO interface originates from oxygen vacancies generated at the surface of the TiO bottom layer during ALD of the AlO overlayer. High-density electrons (∼10 cm) are confined within a ∼2.2 nm distance from the AlO/TiO interface, resulting in a high on-current of ∼12 μA/μm. The ultrathin TiO bottom layer is easy to fully deplete, allowing an extremely low off-current, a high on/off current ratio over 10, and a low subthreshold swing of ∼100 mV/decade. Via the implementation of ALD, a mature thin-film process can facilitate mass production as well as three-dimensional integration of the devices.
The resistive switching behavior in resistive random access memories (RRAMs) using atomic-layer-deposited Ga 2 O 3 / ZnO composite film as the dielectric was investigated. By alternatively atomic-layer-depositing Ga 2 O 3 and ZnO with different thickness, we can accurately control the oxygen vacancy concentration. When regulating ZnO to ∼31%, the RRAMs exhibit a forming-free property as well as outstanding performance, including the ratio of a high resistance state to the low resistance state of 1000, retention time of more than 1 × 10 4 s, and the endurance of 100. By preparing RRAMs of different Zn concentration, we carried out a comparative study and explored the physical origin for the forming-free property as well as good performance. Finally, a unified model is proposed to account for the resistive switching and the current conduction mechanism, providing meaningful insights in the development of high-quality and forming-free RRAMs for future memory and neuromorphic applications.
A two-dimensional electron gas (2DEG) was formed at the interface of an ultrathin Al 2 O 3 /TiO 2 heterostructure that was fabricated using atomic layer deposition (ALD) at a low temperature (<300 °C) on a thermally oxidized SiO 2 /Si substrate. A high electron density (∼10 14 cm −2 ) and mobility (∼4 cm 2 V −1 s −1 ) were achieved, which are comparable to those of the epitaxial LaAlO 3 /SrTiO 3 heterostructure. An in situ resistance measurement directly demonstrated that the resistance of the heterostructure interface dropped significantly with the injection of trimethylaluminum (TMA), indicating that oxygen vacancies were formed on the TiO 2 surface during the TMA pulse in the ALD of Al 2 O 3 films, such that they provide electron donor states to generate free electrons at the interface of the ultrathin Al 2 O 3 /TiO 2 heterostructure. The activation energy of the electron donor states to move to the Ti 3d conduction band plays an essential role in the electrical characteristics of the 2DEG. Interestingly, the donor state level can be tailored by the control of TiO 2 crystallinity, which eventually adjusts the electron density. The activation energy was decreased to less than 20 meV to generate ultrashallow donor states while improving the TiO 2 crystallinity, such that the 2D electrons become readily delocalized, even at room temperature, to create a 2DEG.
Focused ion beam (FIB) is a high-precision technology for micro/nanofabrication that can be used to fabricate micro/nanoscale structures and electronic devices, such as waveguide gratings, resonators, and photonic crystals. In this study, a novel FIB processing system was developed using machine vision coupled with a piezoelectric motor, which compensates the process periodically and automatically. The FIB system is controlled by a computer program that enables automatic processing, automatic recognition, and provides feedback to control the movement of the stage. The results show that ring arrays with a diameter of 2 μm can be detected automatically under the field of view (FOV) of 114 × 114 μm2 with relative errors of less than 6%. The FOV can be larger than 400 × 400 μm2 after the splicing function of automatic compensation control is applied to the same ring arrays. Structurally, the average splicing errors in the X- and Y-directions decreased one order of magnitude, which are from 1.49 to 0.15 μm and 1.47 to 0.37 μm, respectively. This paves the way for the mass production of nanoholes in a large area with high precision and high speed for semiconductor manufacturing and research.
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