Driven by an ever‐expanding interest in new material systems with new functionality, the growth of atomic‐scale electronic materials by molecular beam epitaxy (MBE) has evolved continuously since the 1950s. Here, a new MBE technique called
This content will become publicly available on September 11, 2025
Transparent oxide thin film transistors (TFTs) are an important ingredient of transparent electronics. Their fabrication at the back‐end‐of‐line (BEOL) opens the door to novel strategies to more closely integrate logic with memory for data‐intensive computing architectures that overcome the scaling challenges of today's integrated circuits. A recently developed variant of molecular‐beam epitaxy (MBE) called suboxide MBE (S‐MBE) is demonstrated to be capable of growing epitaxial In2O3at BEOL temperatures with unmatched crystal quality. The fullwidth at halfmaximum of the rocking curve is 0.015° and, thus, ≈5x narrower than any reports at any temperature to date and limited by the substrate quality. The key to achieving these results is the provision of an In2O beam by S‐MBE, which enables growth in adsorption control and is kinetically favorable. To benchmark this deposition method for TFTs, rudimentary devices were fabricated.
more » « less- Award ID(s):
- 1719875
- PAR ID:
- 10548183
- Publisher / Repository:
- Wiley Online Library
- Date Published:
- Journal Name:
- Advanced Electronic Materials
- ISSN:
- 2199-160X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract hybrid ‐MBE (h MBE) is reviewed that has been proven a powerful approach for tackling the challenge of growing high‐quality, multicomponent complex oxides, specifically theAB O3perovskites. The goal of this work is to (1) discuss the development ofh MBE in a historical context, (2) review the advantageous surface kinetics and chemistry that enable the self‐regulated growth ofAB O3perovskites, (3) layout the key components and technical challenges associated withh MBE, (4) review the status of the field and the materials that have been successfully grown byh MBE which demonstrate its general applicability, and (5) discuss the future ofh MBE in regards to technical innovations and expansion into new material classes, which are aimed at expanding into industrial realm and at tackling new scientific endeavors. -
more » « less
Abstract In metal‐oxide thin‐film transistors (TFTs), high‐
k gate dielectrics often yield a higher electron mobility than SiO2. However, investigations regarding the mechanism of this high‐k “mobility boost” are relatively scarce. To explore this phenomenon, solution‐processed In2O3TFTs are fabricated using eight different gate dielectrics (SiO2, Al2O3, ZrO2, HfO2, and bilayer SiO2/high‐k structures). With these structures, the total gate capacitance can be varied independently from the semiconductor–dielectric interface to study this mobility enhancement. It is shown that the mobility enhancement is a combination of the effects of areal gate capacitance and interface quality for disordered oxide semiconductor devices. The ZrO2‐gated TFTs achieve the highest mobility by inducing more accumulation charge with higher gate capacitance. Surprisingly, however, when the gate capacitance is held constant, no mobility enhancement is observed with the high‐k gate dielectrics compared to SiO2. -
more » « less
Abstract This work provides the details of a simple and reliable method with less damage to prepare electron transparent samples for in situ studies in scanning/transmission electron microscopy. In this study, we use epitaxial VO2thin films grown on c‐Al2O3by pulsed laser deposition, which have a monoclinic–rutile transition at ~68°C. We employ an approach combining conventional mechanical wedge‐polishing and Focused Ion beam to prepare the electron transparent samples of epitaxial VO2thin films. The samples are first mechanically wedge‐polished and ion‐milled to be electron transparent. Subsequently, the thin region of VO2films are separated from the rest of the polished sample using a focused ion beam and transferred to the in situ electron microscopy test stage. As a critical step, carbon nanotubes are used as connectors to the manipulator needle for a soft transfer process. This is done to avoid shattering of the brittle substrate film on the in situ sample support stage during the transfer process. We finally present the atomically resolved structural transition in VO2films using this technique. This approach significantly increases the success rate of high‐quality sample preparation with less damage for in situ studies of thin films and reduces the cost and instrumental/user errors associated with other techniques.
The present work highlights a novel, simple, reliable approach with reduced damage to make electron transparent samples for atomic‐scale insights of temperature‐dependent transitions in epitaxial thin film heterostructures using in situ TEM studies.
-
more » « less
We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow α-(AlxGa1−x)2O3 films on (110) sapphire substrates over the 0 < x < 0.95 range of aluminum content. In S-MBE, 99.98% of the gallium-containing molecular beam arrives at the substrate in a preoxidized form as gallium suboxide (Ga2O). This bypasses the rate-limiting step of conventional MBE for the growth of gallium oxide (Ga2O3) from a gallium molecular beam and allows us to grow fully epitaxial α-(AlxGa1−x)2O3 films at growth rates exceeding 1 µm/h and relatively low substrate temperature (Tsub = 605 ± 15 °C). The ability to grow α-(AlxGa1−x)2O3 over the nominally full composition range is confirmed by Vegard’s law applied to the x-ray diffraction data and by optical bandgap measurements with ultraviolet–visible spectroscopy. We show that S-MBE allows straightforward composition control and bandgap selection for α-(AlxGa1−x)2O3 films as the aluminum incorporation x in the film is linear with the relative flux ratio of aluminum to Ga2O. The films are characterized by atomic-force microscopy, x-ray diffraction, and scanning transmission electron microscopy (STEM). These α-(AlxGa1−x)2O3 films grown by S-MBE at record growth rates exhibit a rocking curve full width at half maximum of ≊ 12 arc secs, rms roughness <1 nm, and are fully commensurate for x ≥ 0.5 for 20–50 nm thick films. STEM imaging of the x = 0.78 sample reveals high structural quality and uniform composition. Despite the high structural quality of the films, our attempts at doping with silicon result in highly insulating films.
-
more » « less
Metal oxide (MO) semiconductor thin films prepared from solution typically require multiple hours of thermal annealing to achieve optimal lattice densification, efficient charge transport, and stable device operation, presenting a major barrier to roll-to-roll manufacturing. Here, we report a highly efficient, cofuel-assisted scalable combustion blade-coating (CBC) process for MO film growth, which involves introducing both a fluorinated fuel and a preannealing step to remove deleterious organic contaminants and promote complete combustion. Ultrafast reaction and metal–oxygen–metal (M-O-M) lattice condensation then occur within 10–60 s at 200–350 °C for representative MO semiconductor [indium oxide (In2O3), indium-zinc oxide (IZO), indium-gallium-zinc oxide (IGZO)] and dielectric [aluminum oxide (Al2O3)] films. Thus, wafer-scale CBC fabrication of IGZO-Al2O3thin-film transistors (TFTs) (60-s annealing) with field-effect mobilities as high as ∼25 cm2V−1s−1and negligible threshold voltage deterioration in a demanding 4,000-s bias stress test are realized. Combined with polymer dielectrics, the CBC-derived IGZO TFTs on polyimide substrates exhibit high flexibility when bent to a 3-mm radius, with performance bending stability over 1,000 cycles.
