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 (V_th) 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 V_th. 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 (V_G) of ±5 V demonstrated the stable value of V_th. 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.