Abstract
Amorphous oxide semiconductor (AOS)-based Schottky diodes have been utilized for selectors in crossbar array memories to improve cell-to-cell uniformity with a low-temperature process. However, thermal instability at interfaces between the AOSs and metal electrodes can be a critical issue for the implementation of reliable Schottky diodes. Under post-fabrication annealing, an excessive redox reaction at the ohmic interface can affect the bulk region of the AOSs, inducing an electrical breakdown of the device. Additionally, structural relaxation (SR) of the AOSs can increase the doping concentration at the Schottky interface, which results in a degradation of the rectifying performance. Here, we improved the thermal stability at AOS/metal interfaces by regulating the oxygen vacancy (VO) concentration at both sides of the contact. For a stable quasi-ohmic contact, a Cu-Mn alloy was introduced instead of a single component reactive metal. As Mn only takes up O in amorphous In-Ga-Zn-O (a-IGZO), excessive VO generation in bulk region of a-IGZO can be prevented. At the Schottky interfaces, the barrier characteristics were not degraded by thermal annealing as the Ga concentration in a-IGZO increased. Ga not only reduces the inherent VO concentration but also retards SR, thereby suppressing tunneling conduction and enhancing the thermal stability of devices.
Highlights
As the downsizing of devices increases, the nonuniform properties of crystalline semiconductors caused by grain boundaries can be an issue in the consideration of cell-to-cell uniformity in crossbar circuits[6,11]
We have developed a thermally stable amorphous In-GaZn-O (a-IGZO) Schottky diode through both the regulation of the interface reduction reaction at the ohmic contact and the structural relaxation (SR)-driven electron doping of a-IGZO at the Schottky contact
The CuMn (2 at% Mn) alloy forms a thermally stable ohmic contact because only the small amount of Mn induces the interfacial reduction of a-IGZO during post-fabrication annealing and suppresses excessive VO generation in a-IGZO, which affects the bulk resistance
Summary
As the downsizing of devices increases, the nonuniform properties of crystalline semiconductors caused by grain boundaries can be an issue in the consideration of cell-to-cell uniformity in crossbar circuits[6,11]. In this respect, amorphous oxide semiconductor (AOS)-based Schottky diodes have been recently developed because of their long-range disorder-related unique properties, enhanced uniform electrical properties and mechanical flexibility with a low-temperature fabrication process[12,13,14,15], which has merits for flexible[16,17] and large-area applications[18,19]. When the interfacial reactions are not regulated, the doping concentration in the bulk region of the AOSs will be affected by the interfacial reactions, thereby inducing a breakdown of the devices as well as degrading ΦB
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