Benzylphosphonic acid treated ultra-thin ALD-InOx for long term device stability

Abstract

In this paper, we demonstrate the long-term stability of the threshold voltage (Vth) of ultra-thin indium oxide (In2O3) TFTs fabricated by atomic layer deposition (ALD) and modified with self-assembled monolayers (SAMs) of benzylphosphonic acid (BPA). By forming a self-assembled monolayer of BPA, it was possible to modify the surface to be hydrophobic and to have a lower surface energy as low as 24 mJ m？2. The surface-modified TFTs were found to be very stable for 168 hours in air with negligible change in Vth. In addition, the subthreshold swing (S.S.) and hysteresis showed improved electrical characteristics. Furthermore, the positive and negative bias stress (PBS and NBS) measurements at 3000 s and a gate voltage (VG) of ±5 V demonstrated the stable value of Vth. This is due to the strong covalent bonding of the hydroxyl group (？OH) on the surface BPA and In2O3 back-channel, which avoids chemisorption of oxygen (O2) and water (H2O) molecules from ambient air and reduces the degradation of the electrical properties of the TFT. These results demonstrate the promising stability of long-term electrical properties and the ease of application to ultra-thin In2O3 TFT and other oxide semiconductors.