Nano-Laminated Metal Oxides/Polyamide Stretchable Moisture- and Gas-Barrier Films by Integrated Atomic/Molecular Layer Deposition.

Stretchable barrier films capable of maintaining high levels of moisture- and gas-barrier performance under significant mechanical strains are a critical component for wearable/flexible electronics and other devices, but realization of stretchable moisture-barrier films has not been possible due to the inevitable issues of strain-induced rupturing compounded with moisture-induced swelling of a stretched barrier film. This study demonstrates nanolaminated polymer/metal oxide stretchable moisture-barrier films fabricated by a novel molecular layer deposition (MLD) process of polyamide-2,3 (PA-2,3) integrated with atomic layer deposition (ALD) metal oxide processes and an in situ surface-functionalization technique. The PA-2,3 surface upon in situ functionalization with H2O2 vapor offers adequate surface chemisorption sites for rapid nucleation of ALD oxides, minimizing defects at the PA-2,3/oxide interfaces in the nanolaminates. The integrated ALD/MLD process enables facile deposition and precise structural control of many-layered oxide/PA-2,3 nanolaminates, where the large number of PA-2,3 nanolayers provide high tolerance against mechanical stretching and flexing thanks to their defect-decoupling and stress-buffering functions, while the large number of oxide nanolayers shield against swelling by moisture. Specifically, a nanolaminate with 72 pairs of alternating 2 nm (5 cycles) PA-2,3 and 0.5 nm HfO2 (five cycles) maintains its water vapor transmission rate (WVTR) at the 10-6 g/m2 day level upon 10% tensile stretching and 2 mm-radius bending, a significant breakthrough for the wearable/flexible electronics technologies.

Low-temperature gas-barrier films by atomic layer deposition for encapsulating organic light-emitting diodes.

Dependences of gas-barrier performance on the deposition temperature of atomic-layer-deposited (ALD) Al2O3, HfO2, and ZnO films were studied to establish low-temperature ALD processes for encapsulating organic light-emitting diodes (OLEDs). By identifying and controlling the key factors, i.e. using H2O2 as an oxidant, laminating Al2O3 with HfO2 or ZnO layers into AHO or AZO nanolaminates, and extending purge steps, OLED-acceptable gas-barrier performance (water vapor transmission rates ∼ 10-6 g m-2 d-1) was achieved for the first time at a low deposition temperature of 50 °C in a thermal ALD mode. The compatibility of the low-temperature ALD process with OLEDs was confirmed by applying the process to encapsulate different types of OLED devices, which were degradation-free upon encapsulation and showed adequate lifetime during accelerated aging tests (pixel shrinkage <5% after 240 h at 60 °C/90% RH).

Stable and High-Performance Flexible ZnO Thin-Film Transistors by Atomic Layer Deposition.

Passivation is a challenging issue for the oxide thin-film transistor (TFT) technologies because it requires prolonged high-temperature annealing treatments to remedy defects produced in the process, which greatly limits its manufacturability as well as its compatibility with temperature-sensitive materials such as flexible plastic substrates. This study investigates the defect-formation mechanisms incurred by atomic layer deposition (ALD) passivation processes on ZnO TFTs, based on which we demonstrate for the first time degradation-free passivation of ZnO TFTs by a TiO2/Al2O3 nanolaminated (TAO) film deposited by a low-temperature (110 °C) ALD process. By combining the TAO passivation film with ALD dielectric and channel layers into an integrated low-temperature ALD process, we successfully fabricate flexible ZnO TFTs on plastics. Thanks to the exceptional gas-barrier property of the TAO film (water vapor transmission rate (WVTR)<10(-6) g m(-2) day(-1)) as well as the defect-free nature of the ALD dielectric and ZnO channel layers, the TFTs exhibit excellent device performance with high stability and flexibility: field-effect mobility>20 cm2 V(-1) s(-1), subthreshold swing<0.4 V decade(-1) after extended bias-stressing (>10,000 s), air-storage (>1200 h), and bending (1.3 cm radius for 1000 times).

Air-stable flexible organic light-emitting diodes enabled by atomic layer deposition.

Organic light-emitting diodes (OLED) are an energy-efficient light source with many desirable attributes, besides being an important display of technology, but its practical application has been limited by its low air-stability. This study demonstrates air-stable flexible OLEDs by utilizing two atomic-layer-deposited (ALD) films: (1) a ZnO film as both a stable electron-injection layer (EIL) and as a gas barrier in plastics-based OLED devices, and (2) an Al2O3/ZnO (AZO) nano-laminated film for encapsulating the devices. Through analyses of the morphology and electrical/gas-permeation properties of the films, we determined that a low ALD temperature of 70 °C resulted in optimal EIL performance from the ZnO film and excellent gas-barrier properties [water vapor transmission rate (WVTR) <5 × 10(-4) g m(-2) day(-1)] from both the ZnO EIL and the AZO encapsulating film. The low-temperature ALD processes eliminated thermal damage to the OLED devices, which were severe when a 90 °C encapsulation process was used, while enabling them to achieve an air-storage lifetime of >10,000 h.

Transparent conductive gas-permeation barriers on plastics by atomic layer deposition.

A mixed-deposition atomic layer deposition process produces Hf:ZnO films with uniform dopant distribution and high electrical conductivity (resistivity = 4.5 × 10(-4) W cm), optical transparency (>85% from 400-1800 nm), and moisture-barrier property (water vapor transmission rate = 6.3 × 10(-6) g m(-2) day(-1)).