Organic/Inorganic Hybrid Buffer in InGaZnO Transistors under Repetitive Bending Stress for High Electrical and Mechanical Stability

Abstract

We investigated the influence of the multilayered hybrid buffer consisting of Al2O3/PA (polyacrylic) organic layer/Al2O3 on the electrical and mechanical properties of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs). The multilayered organic/inorganic hybrid buffer has multiple beneficial effects on the flexible TFTs under repetitive bending stress. First, compared to the PA or Al2O3 single-layered buffer, the multilayered hybrid buffer showed an improved WVTR value of 1.1 × 10–4 g/m2 day. Even after 40,000 bending cycles, the WVTR value of the hybrid buffer increased only by 17%, while the WVTR value of the Al2O3 layer doubled after cyclical bending stress. We also confirmed that the hybrid buffer has advantages in mechanical durability of the TFT layers because of the change in the position of the neutral plane and the strain reduction effect by the PA organic layer. When we fabricate a top-gate a-IGZO TFT with the hybrid buffer layer (HB TFT), the device shows V th = 0.74 V, μFE = 14.4 cm2/V·s, a subthreshold slope of 0.27 V/dec, and hysteresis of 0.21 V, which are superior to that of TFTs fabricated on an Al2O3 single-layer buffer (IB TFT). From the X-ray photoelectron spectroscopy and elastic recoil detection analysis, the difference in the electrical performance of TFTs could be explained by hydrogen-related molecules. After annealing at 270 °C, the amounts of hydrogen found in the a-IGZO layer for the IB, HB, and OB TFTs were 3.57 × 1021, 5.77 × 1021, and 7.34 × 1021 atoms/cm3, respectively. A top-gate bottom-contact structured a-IGZO TFT fabricated on the PA layer (OB TFT) showed a gate dielectric breakdown because of excessively high hydrogen content and high nonbonding oxygen content. On the other hand, HB TFTs showed better positive bias stability because of the higher hydrogen concentration, as hydrogen (when not excessive) is beneficial in passivating electron traps. Finally, we conducted 60,000 repetitive bending cycles on IB TFTs and HB TFTs with various bending radii down to 1.5 mm. The HB TFT shows improved mechanical durability and exhibits less electrical degradation during and after repetitive bending stress, compared to the IB TFT.

Self-Assembled Nanodielectrics for Solution-Processed Top-Gate Amorphous IGZO Thin-Film Transistors

“…16 The well-known sensitivity of a-IGZO to atmospheric effects is known to contribute to device instability and is a major attraction of top-gate devices. 37,48,66 Numerous studies have reported improved environmental stability of top-gate a-IGZO TFTs using a variety of dielectric materials. 41,43,60,69 It is therefore expected that the top-gate SAND TFTs will have superior environmental stability compared to bottom-gate devices.…”

Highly Scalable and Robust Mesa‐Island‐Structure Metal‐Oxide Thin‐Film Transistors and Integrated Circuits Enabled by Stress‐Diffusive Manipulation

“…[ 21,22 ] Also, adopting an organic/inorganic hybrid buffer layer in a top‐gate a‐IGZO TFT has shown improved mechanical stability by changing the stress distribution in the device. [ 23 ] In addition, adopting more flexible carbon‐based materials for a‐IGZO TFT‐based amplifiers on an ultrathin (<3 µm) PI substrate also allowed the demonstration of flexible metal‐oxide/carbon nanotube complementary circuits with reliable electrical and mechanical characteristics. [ 24 ]…”

A Biodegradable Gelatin Substrate and its Application for Crack Suppression of Flexible Gelatin Resistive Memory Device

“…Although flexible electronic is achieving a great variety of applications, [ 1–4 ] most of them were suffered from the device performance degradation caused by bending over time. [ 5–7 ] This issue was related to bending can result in the generation of cracks. [ 8 – 10 ]…”