Semiconductor Devices & Physics Laboratory

(반도체소자물리연구실)

Welcome to Semiconductor Devices & Physics Laboratory (SDPL) at Soongsil University!
Our research covers semiconductor material science, device fabrication, and system integration.

대학원 (학석연계, 석사과정, 박사과정 및 석박통합과정) 진학 문의: 오홍석 교수 (hoh@ssu.ac.kr)

(학부 연구생은 TO가 없습니다)

Physical Reservoir Computing Using Tellurium-Based Gate-Tunable Artificial Photonic Synapses

We report tellurium thin-film-based artificial photonic synapses and their application to physical reservoir computing, in ACS Nano. Reservoir computing is a computing framework that achieves energy-efficient AI computation by pre-processing data with a reservoir—a fixed, randomly connected network. Physical reservoir computing replaces this network with a physical system, significantly reducing energy consumption. Our research demonstrates that tellurium (an emerging p-type material)-based photonic synapses can effectively serve as a physical reservoir. We demonstrated two applications: Classification of hand-written digits (no binarization!), and prediction of solutions for a second-order non-linear system.

We appreciate the strong collaboration with the research groups of Prof. Mun Seok Jeong and Prof. Jin Pyo Hong at Hanyang University. (Correspondence: Prof. Oh at Soonsgil University, Prof. Jeong and Prof. Hong at Hanyang University)

Highly sensitive and fast responding flexible force sensors using ZnO/ZnMgO coaxial nanotubes on graphene layers for breath sensing

We report the fabrication of highly sensitive, rapidly responding flexible force sensors and their applications in sleep apnea monitoring, in Advanced Healthcare Materials. The sensor utilized Position- and morphology-controlled ZnO nanotubes which were heteroepitaxially grown on multilayer graphene layers. Flexible force sensors were fabricated by forming Schottky contacts to the nanotube array, followed by the mechanical release of the entire structure from the host substrate. The electrical characteristics of ZnO and ZnO/ZnMgO nanotube-based sensors are thoroughly investigated and compared. Importantly, in force sensor applications, the ZnO/ZnMgO coaxial structure resulted in significantly higher sensitivity and a faster response time when compared to the bare ZnO nanotube. The origin of the improved performance is thoroughly discussed. Furthermore, wireless breath sensing is demonstrated using the ZnO/ZnMgO pressure sensors with custom electronics, demonstrating the feasibility of the sensor technology for health monitoring and the potential diagnosis of sleep apnea. We appreciate the invaluable collaboration with Prof. Yi's group at SNU!
(Correspondence: Prof. Yi at Seoul National University and Prof. Oh at Soongsil University)

Flexible Photonic Synapses Using Vertical ZnO Nanotubes on Graphene Films

We report the fabrication and characterization of flexible photonic synapses, in IEEE Journal of Selected Topics in Quantum Electronics. Position- and morphology-controlled ZnO nanotubes were heteroepitaxially grown on multilayer graphene layers and served as flexible channels for synaptic devices. Current–voltage characterizations under different light illumination conditions, as well as a study of the temperature-dependent transient photocurrent, revealed the origin of persistent photoconductivity of the device. Importantly, the device exhibited excellent synaptic properties upon application of light pulses, such as excitatory post-synaptic currents and paired pulse facilitations. For the long-term plasticity, potentiation-depression characteristics with high linearity were successfully implemented with good reliability. These features were observed even under different bending conditions, confirming the flexibility of the device. A simulation study suggested that the device will exhibit excellent performance when integrated into neural network structures. We appreciate Prof. Yi's group at SNU for the synergetic collaboration.
(Correspondence: Prof. Oh at Soongsil University and Prof. Yi at Seoul National University)

IGZO thin-film transistors with tunneling contacts: towards power efficient display

We present the fabrication of IGZO TFTs featuring tunneling contacts, in Applied Physics Express. These devices display fast saturation and dimension-invariant current scaling, attributed to a unique current injection mechanism. Notably, the device demonstrates a dual current saturation mechanism: one resulting from the development of a depletion envelope at the source-side and another from the depletion of the accumulation channel at the drain side. The fabrication of these devices is achieved using standard RF magnetron sputtering, which includes the production of the tunneling barrier layer. This suggests the potential for scalable fabrication of contact-engineered devices, which could contribute to the development of future power-efficient TFT technology intended for display applications.

MeaSSUre:I-V, a open software for transistor characterization

We introduce new open software named "MeaSSUre:I-V", a software for transistor characterization using source-meter units (such as Model 2400), in the journal SoftwareX. It allows users to measure transfer & output curves of field-effect transistors, collector characteristics of bipolar junction transistors, or a simple two-terminal I-V curves. You can access to the repository here, or directly download the program here.

IGZO synaptic TFT with embedded AlOx charge trap layers:

We report the fabrication of synaptic thin-film transistor using embedded AlOx layer in IGZO thin-film channel, in the journal Applied Physics Express. The fabricated device exhibited excellent synaptic characteristics such as excitatory post-synaptic current, paired-pulse facilitation, and potentiation-depression by electric pulse. Simulation study validated the efficiency of the fabricated device. Importantly, the research was lead by the undergraduate student intern (Yeojin Lee)!

"My definition of physics is that physics is not what you’re working on, but how you’re working on it.
If you have the attitude of someone who comes from physics, it’s a physics problem." - John Hopfield

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