Research Bits: April 16

Tunable thermal conductivity in memristors; amorphous oxide semiconductor contact resistance; active titanium dioxide substrate.


Tunable thermal conductivity in memristors

Researchers from the Center for Research in Biological Chemistry and Molecular Materials (CiQUS) and Forschungszentrum Juelich discovered that oxide-based memristive devices can demonstrate tunable thermal conductivity.

Alongside the memristor’s electrical resistive switching, a thermal resistive switching effect also occurs at the metal-oxide interface of the material, due to the accumulation of oxygen ions. This alteration in heat flow resistance can be modulated by around 20% at room temperature.

“Oxides are materials with thermal resistance highly sensitive to oxygen concentration, so by inducing a displacement of these ions when an electric field is applied, we modify their thermal properties,” said Víctor Álvarez, a PhD candidate at CiQUS, in a statement. “Depending on the resistive state of the device, we’ve achieved a reversible increase or decrease in thermal conductivity with an electric field.”

The team aims to develop new thermoregulators based on controlling ion movement in dielectric oxides. [1]

Amorphous oxide semiconductor contact resistance

Researchers from the Tokyo Institute of Technology and National Institute for Materials Science developed a way to reduce contact resistance in amorphous oxide semiconductor (AOS) storage devices by using palladium to inject hydrogen into the deeply buried oxide-metal electrode contacts.

Thin film transistors (TFTs) based on AOSs have applications in capacitor-less and high-density DRAM. However, contact issues between the AOS and electrodes result in high contact resistance with degraded charge carrier mobility and increased power consumption, particularly when vertically stacked.

Hydrogen injected into the AOS-electrode contact area generates charge carriers, thereby reducing contact resistance. The team’s method uses palladium (Pd), which can catalyze the dissociation of hydrogen at low temperatures. “The team fabricated amorphous indium gallium oxide (a-IGZO) TFTs with Pd thin film electrodes as hydrogen transport pathways. The TFTs were heat-treated in a 5% hydrogen atmosphere at a temperature of 150 ℃ for 10 minutes,” the researchers noted in a statement. “This resulted in the transport of atomic hydrogen by Pd to the a-IGZO-Pd interface, triggering a reaction between oxygen and hydrogen, forming a highly conductive interfacial layer. The contact resistance of the TFTs was reduced by two orders of magnitude, while charge carrier mobility increased from 3.2 cm2V-1s-1 to nearly 20 cm2V-1s-1.” [2]

Active titanium dioxide substrate

Researchers from Pennsylvania State University, Cornell University, Argonne National Laboratory, Paul-Drude-Institut für Festkörperelektronik, and Georgia Institute of Technology found that some semiconductor substrates can respond to electrical changes.

While investigating the semiconductor vanadium dioxide, which is capable of very fast switching, the researchers found that it interacts with the substrate material titanium dioxide. There appears to be an active layer in the substrate that behaves similarly to the semiconductor material on top of it when the semiconductor switches between an insulator and a metal.

“What we found was that as the vanadium dioxide film changes to a metal, the whole film channel bulges, which is very surprising. Normally it is supposed to shrink. So clearly something else was going on in the film geometry that was missed before,” said Venkatraman Gopalan, professor of materials science and engineering and of physics at Penn State, in a release. “We found to our great surprise that this substrate is very much active, jiving and responding in completely surprising ways as the film switches from an insulator to a metal and back, when the electrical pulses arrive.” [3]


[1] Víctor Álvarez-Martínez, Rafael Ramos, Víctor Leborán, Alexandros Sarantopoulos, Regina Dittmann, and Francisco Rivadulla, Interfacial Thermal Resistive Switching in (Pt,Cr)/SrTiO3 Devices. ACS Applied Materials & Interfaces 2024 16 (12), 15043-15049

[2] Yuhao Shi, Masatake Tsuji, Hanjun Cho, Shigenori Ueda, Junghwan Kim, and Hideo Hosono, Approach to Low Contact Resistance Formation on Buried Interface in Oxide Thin-Film Transistors: Utilization of Palladium-Mediated Hydrogen Pathway. ACS Nano 2024 18 (13), 9736-9745

[3] G. Stone, Y. Shi, M. Jerry, V. Stoica, H. Paik, Z. Cai, D. G. Schlom, R. Engel-Herbert, S. Datta, H. Wen, L.-Q. Chen, V. Gopalan, In-Operando Spatiotemporal Imaging of Coupled Film-Substrate Elastodynamics During an Insulator-to-Metal Transition. Adv. Mater. 2024, 2312673.

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