19 results on '"Sangsig Kim"'
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2. Binarized neural network of diode array with high concordance to vector–matrix multiplication
- Author
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Yunwoo Shin, Kyoungah Cho, and Sangsig Kim
- Subjects
Binarized neural network ,Multiply-accumulate ,Vector–matrix multiplication ,Gated p+-n-p-n+ diodes ,Positive-feedback loop mechanism ,Medicine ,Science - Abstract
Abstract In this study, a binarized neural network (BNN) of silicon diode arrays achieved vector–matrix multiplication (VMM) between the binarized weights and inputs in these arrays. The diodes that operate in a positive-feedback loop in their p+-n-p-n+ device structure possess steep switching and bistable characteristics with an extremely low subthreshold swing (below 1 mV) and a high current ratio (approximately 108). Moreover, the arrays show a self-rectifying functionality and an outstanding linearity by an R-squared value of 0.99986, which allows to compose a synaptic cell with a single diode. A 2 × 2 diode array can perform matrix multiply-accumulate operations for various binarized weight matrix cases with some input vectors, which is in high concordance with the VMM, owing to the high reliability and uniformity of the diodes. Moreover, the disturbance-free, nondestructive readout, and semi-permanent holding characteristics of the diode arrays support the feasibility of implementing the BNN.
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- 2024
- Full Text
- View/download PDF
3. Universal logic-in-memory cell enabling all basic Boolean algebra logic
- Author
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Eunwoo Baek, Kyoungah Cho, and Sangsig Kim
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Medicine ,Science - Abstract
Abstract Among the promising approaches for implementing high-performance computing, reconfigurable logic gates and logic-in-memory (LIM) approaches have been drawing increased research attention. These allow for improved functional scaling of a chip, owing to the improved functionality per unit area. Although numerous studies have been conducted independently for either reconfigurable logic or LIM units, attempts to construct a hybrid structure based on reconfigurable logic and LIM units remain relatively rare. In this study, we merge reconfigurable logic gates and LIM units to achieve a universal logic-in-memory (ULIM) cell for enabling all basic Boolean logic operations and data storage in a single cell. A ULIM cell consisting of silicon memory devices with reconfigurable n- and p-program modes can reconfigure logic operations within the complete set of Boolean logic operations. Moreover, the ULIM cell exhibits memory behaviors for storing output logic values without supply voltages for a certain period, resulting in zero static power consumption. Hence, this study provides a way to realize high-performance electronics by utilizing the silicon devices with a hybrid function of reconfigurable logic and LIM.
- Published
- 2022
- Full Text
- View/download PDF
4. Logic and memory functions of an inverter comprising reconfigurable double gated feedback field effect transistors
- Author
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Juhee Jeon, Sola Woo, Kyoungah Cho, and Sangsig Kim
- Subjects
Medicine ,Science - Abstract
Abstract In this study, we propose an inverter consisting of reconfigurable double-gated (DG) feedback field-effect transistors (FBFETs) and examine its logic and memory operations through a mixed-mode technology computer-aided design simulation. The DG FBFETs can be reconfigured to n- or p-channel modes, and these modes exhibit an on/off current ratio of ~ 1012 and a subthreshold swing (SS) of ~ 0.4 mV/dec. Our study suggests the solution to the output voltage loss, a common problem in FBFET-based inverters; the proposed inverter exhibits the same output logic voltage as the supply voltage in gigahertz frequencies by applying a reset operation between the logic operations. The inverter retains the output logic ‘1’ and ‘0’ states for ~ 21 s without the supply voltage. The proposed inverter demonstrates the promising potential for logic-in-memory application.
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- 2022
- Full Text
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5. New ternary inverter with memory function using silicon feedback field-effect transistors
- Author
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Jaemin Son, Kyoungah Cho, and Sangsig Kim
- Subjects
Medicine ,Science - Abstract
Abstract In this study, we present a fully complementary metal–oxide–semiconductor-compatible ternary inverter with a memory function using silicon feedback field-effect transistors (FBFETs). FBFETs operate with a positive feedback loop by carrier accumulation in their channels, which allows to achieve excellent memory characteristics with extremely low subthreshold swings. This hybrid operation of the switching and memory functions enables FBFETs to implement memory operation in a conventional CMOS logic scheme. The inverter comprising p- and n-channel FBFETs in series can be in ternary logic states and retain these states during the hold operation owing to the switching and memory functions of FBFETs. It exhibits a high voltage gain of approximately 73 V/V, logic holding time of 150 s, and reliable endurance of approximately 105. This ternary inverter with memory function demonstrates possibilities for a new computing paradigm in multivalued logic applications.
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- 2022
- Full Text
- View/download PDF
6. Neural oscillation of single silicon nanowire neuron device with no external bias voltage
- Author
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Sola Woo and Sangsig Kim
- Subjects
Medicine ,Science - Abstract
Abstract In this study, we perform simulations to demonstrate neural oscillations in a single silicon nanowire neuron device comprising a gated p–n–p–n diode structure with no external bias lines. The neuron device emulates a biological neuron using interlinked positive and negative feedback loops, enabling neural oscillations with a high firing frequency of ~ 8 MHz and a low energy consumption of ~ 4.5 × 10−15 J. The neuron device provides a high integration density and low energy consumption for neuromorphic hardware. The periodic and aperiodic patterns of the neural oscillations depend on the amplitudes of the analog and digital input signals. Furthermore, the device characteristics, energy band diagram, and leaky integrate-and-fire operation of the neuron device are discussed.
- Published
- 2022
- Full Text
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7. NAND and NOR logic-in-memory comprising silicon nanowire feedback field-effect transistors
- Author
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Yejin Yang, Juhee Jeon, Jaemin Son, Kyoungah Cho, and Sangsig Kim
- Subjects
Medicine ,Science - Abstract
Abstract The processing of large amounts of data requires a high energy efficiency and fast processing time for high-performance computing systems. However, conventional von Neumann computing systems have performance limitations because of bottlenecks in data movement between separated processing and memory hierarchy, which causes latency and high power consumption. To overcome this hindrance, logic-in-memory (LIM) has been proposed that performs both data processing and memory operations. Here, we present a NAND and NOR LIM composed of silicon nanowire feedback field-effect transistors, whose configuration resembles that of CMOS logic gate circuits. The LIM can perform memory operations to retain its output logic under zero-bias conditions as well as logic operations with a high processing speed of nanoseconds. The newly proposed dynamic voltage-transfer characteristics verify the operating principle of the LIM. This study demonstrates that the NAND and NOR LIM has promising potential to resolve power and processing speed issues.
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- 2022
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8. Simulation studies on electrical characteristics of silicon nanowire feedback field-effect transistors with interface trap charges
- Author
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Yejin Yang, Young-Soo Park, Jaemin Son, Kyoungah Cho, and Sangsig Kim
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Medicine ,Science - Abstract
Abstract In this study, we examine the electrical characteristics of silicon nanowire feedback field-effect transistors (FBFETs) with interface trap charges between the channel and gate oxide. The band diagram, I–V characteristics, memory window, and operation were analyzed using a commercial technology computer-aided design simulation. In an n-channel FBFET, the memory window narrows (widens) from 5.47 to 3.59 V (9.24 V), as the density of the positive (negative) trap charges increases. In contrast, in the p-channel FBFET, the memory window widens (narrows) from 5.38 to 7.38 V (4.18 V), as the density of the positive (negative) trap charges increases. Moreover, we investigate the difference in the output drain current based on the interface trap charges during the memory operation.
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- 2021
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9. One-transistor static random-access memory cell array comprising single-gated feedback field-effect transistors
- Author
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Sangik Choi, Jaemin Son, Kyoungah Cho, and Sangsig Kim
- Subjects
Medicine ,Science - Abstract
Abstract In this study, we fabricated a 2 × 2 one-transistor static random-access memory (1T-SRAM) cell array comprising single-gated feedback field-effect transistors and examined their operation and memory characteristics. The individual 1T-SRAM cell had a retention time of over 900 s, nondestructive reading characteristics of 10,000 s, and an endurance of 108 cycles. The standby power of the individual 1T-SRAM cell was estimated to be 0.7 pW for holding the “0” state and 6 nW for holding the “1” state. For a selected cell in the 2 × 2 1T-SRAM cell array, nondestructive reading of the memory was conducted without any disturbance in the half-selected cells. This immunity to disturbances validated the reliability of the 1T-SRAM cell array.
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- 2021
- Full Text
- View/download PDF
10. Mechanism of carrier controllability with metal capping layer on amorphous oxide SiZnSnO semiconductor
- Author
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Byeong Hyeon Lee, Ahrum Sohn, Sangsig Kim, and Sang Yeol Lee
- Subjects
Medicine ,Science - Abstract
Abstract The change of electrical performance of amorphous SiZnSnO thin film transistors (a-SZTO TFTs) has been investigated depending on various metal capping layers on the channel layer by causing different contact property. It was confirmed that the change of electrical characteristics was sensitively dependent on the change of the capping layer materials on the same channel layer between the source/drain electrodes. This sensitive change in the electrical characteristics is mainly due to different work function of metal capping layer on the channel layer. The work function of each capping layer material has been analyzed and derived by using Kelvin probe force microscopy and compared with the energy bandgap of the SZTO layer. When the work function of the capping layer is larger than that of the channel layer, electrons are depleted from the channel layer to the capping layer. On the contrary, in the case of using a material having a work function smaller than that of the channel layer, the electrical characteristics were improved because electrons were injected into the channel layer. Based on depletion and injection mechanism caused by different contact barrier between metal capping layer and channel layer, NOT, NAND, and NOR logic circuits have been implemented simply by changing metal capping layer on the channel layer.
- Published
- 2019
- Full Text
- View/download PDF
11. One-transistor static random-access memory cell array comprising single-gated feedback field-effect transistors
- Author
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Jaemin Son, Sangsig Kim, Sangik Choi, and Kyoungah Cho
- Subjects
Multidisciplinary ,Materials science ,Cellular array ,business.industry ,Science ,Reading (computer) ,Transistor ,Electrical engineering ,Article ,Electrical and electronic engineering ,law.invention ,Reliability (semiconductor) ,law ,Electronic devices ,Medicine ,Field-effect transistor ,Static random-access memory ,State (computer science) ,Standby power ,business - Abstract
In this study, we fabricated a 2 × 2 one-transistor static random-access memory (1T-SRAM) cell array comprising single-gated feedback field-effect transistors and examined their operation and memory characteristics. The individual 1T-SRAM cell had a retention time of over 900 s, nondestructive reading characteristics of 10,000 s, and an endurance of 108 cycles. The standby power of the individual 1T-SRAM cell was estimated to be 0.7 pW for holding the “0” state and 6 nW for holding the “1” state. For a selected cell in the 2 × 2 1T-SRAM cell array, nondestructive reading of the memory was conducted without any disturbance in the half-selected cells. This immunity to disturbances validated the reliability of the 1T-SRAM cell array.
- Published
- 2021
12. Neural oscillation of single silicon nanowire neuron device with no external bias voltage
- Author
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Sola Woo and Sangsig Kim
- Subjects
Neurons ,Silicon ,Multidisciplinary ,Computers ,Nanowires - Abstract
In this study, we perform simulations to demonstrate neural oscillations in a single silicon nanowire neuron device comprising a gated p–n–p–n diode structure with no external bias lines. The neuron device emulates a biological neuron using interlinked positive and negative feedback loops, enabling neural oscillations with a high firing frequency of ~ 8 MHz and a low energy consumption of ~ 4.5 × 10−15 J. The neuron device provides a high integration density and low energy consumption for neuromorphic hardware. The periodic and aperiodic patterns of the neural oscillations depend on the amplitudes of the analog and digital input signals. Furthermore, the device characteristics, energy band diagram, and leaky integrate-and-fire operation of the neuron device are discussed.
- Published
- 2021
13. Memory characteristics of silicon nanowire transistors generated by weak impact ionization
- Author
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Sangsig Kim, Yoonjoong Kim, Minsuk Kim, and Doohyeok Lim
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Materials science ,lcsh:Medicine ,02 engineering and technology ,Hardware_PERFORMANCEANDRELIABILITY ,01 natural sciences ,Article ,law.invention ,law ,0103 physical sciences ,Hardware_INTEGRATEDCIRCUITS ,Static random-access memory ,Silicon nanowires ,lcsh:Science ,010302 applied physics ,Multidisciplinary ,Hardware_MEMORYSTRUCTURES ,business.industry ,Transistor ,lcsh:R ,021001 nanoscience & nanotechnology ,Impact ionization ,Subthreshold swing ,Optoelectronics ,lcsh:Q ,0210 nano-technology ,business ,Hardware_LOGICDESIGN - Abstract
In this study, we demonstrate the static random access memory (SRAM) characteristics generated by weak impact ionization in bendable field-effect transistors (FETs) with n+-p-n+ silicon nanowire (SiNW) channels. Our bendable SiNW FETs show not only superior switching characteristics such as an on/off current ratio of ~105 and steep subthreshold swing (~5 mV/dec) but also reliable SRAM characteristics. The SRAM characteristics originate from the positive feedback loops in the SiNW FETs generated by weak impact ionization. This paper describes in detail the operating mechanism of our device and demonstrates the potential of bendable SiNW FETs for future SRAM applications.
- Published
- 2017
14. Investigation on energy bandgap states of amorphous SiZnSnO thin films
- Author
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Kyung Sang Cho, Doo Yong Lee, Byeong Hyeon Lee, Sang-Woo Kim, Ji Ye Lee, Sang Yeol Lee, Ahrum Sohn, Sungkyun Park, Hyuck Choo, and Sangsig Kim
- Subjects
Materials science ,Band gap ,lcsh:Medicine ,Physics::Optics ,02 engineering and technology ,01 natural sciences ,Article ,symbols.namesake ,Condensed Matter::Materials Science ,Engineering ,X-ray photoelectron spectroscopy ,0103 physical sciences ,lcsh:Science ,010302 applied physics ,Kelvin probe force microscope ,Multidisciplinary ,Condensed matter physics ,Condensed Matter::Other ,Electron energy loss spectroscopy ,Fermi level ,lcsh:R ,021001 nanoscience & nanotechnology ,Amorphous solid ,symbols ,Density of states ,lcsh:Q ,0210 nano-technology ,Ultraviolet photoelectron spectroscopy - Abstract
The variation in energy bandgaps of amorphous oxide semiconducting SiZnSnO (a-SZTO) has been investigated by controlling the oxygen partial pressure (Op). The systematic change in Op during deposition has been used to control the electrical characteristics and energy bandgap of a-SZTO. As Op increased, the electrical properties degraded, while the energy bandgap increased systematically. This is mainly due to the change in the oxygen vacancy inside the a-SZTO thin film by controlling Op. Changes in oxygen vacancies have been observed by using X-ray photoelectron spectroscopy (XPS) and investigated by analyzing the variation in density of states (DOS) inside the energy bandgaps. In addition, energy bandgap parameters, such as valence band level, Fermi level, and energy bandgap, were extracted by using ultraviolet photoelectron spectroscopy, Kelvin probe force microscopy, and high-resolution electron energy loss spectroscopy. As a result, it was confirmed that the difference between the conduction band minimum and the Fermi level in the energy bandgap increased systematically as Op increases. This shows good agreement with the measured results of XPS and DOS analyses.
- Published
- 2019
15. Mechanism of carrier controllability with metal capping layer on amorphous oxide SiZnSnO semiconductor
- Author
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Ahrum Sohn, Sangsig Kim, Sang Yeol Lee, and Byeong Hyeon Lee
- Subjects
0301 basic medicine ,Kelvin probe force microscope ,Multidisciplinary ,Materials science ,business.industry ,Science ,NOR logic ,Article ,Amorphous solid ,03 medical and health sciences ,030104 developmental biology ,0302 clinical medicine ,Semiconductor ,Thin-film transistor ,Electrode ,Medicine ,Optoelectronics ,Work function ,sense organs ,business ,Layer (electronics) ,030217 neurology & neurosurgery - Abstract
The change of electrical performance of amorphous SiZnSnO thin film transistors (a-SZTO TFTs) has been investigated depending on various metal capping layers on the channel layer by causing different contact property. It was confirmed that the change of electrical characteristics was sensitively dependent on the change of the capping layer materials on the same channel layer between the source/drain electrodes. This sensitive change in the electrical characteristics is mainly due to different work function of metal capping layer on the channel layer. The work function of each capping layer material has been analyzed and derived by using Kelvin probe force microscopy and compared with the energy bandgap of the SZTO layer. When the work function of the capping layer is larger than that of the channel layer, electrons are depleted from the channel layer to the capping layer. On the contrary, in the case of using a material having a work function smaller than that of the channel layer, the electrical characteristics were improved because electrons were injected into the channel layer. Based on depletion and injection mechanism caused by different contact barrier between metal capping layer and channel layer, NOT, NAND, and NOR logic circuits have been implemented simply by changing metal capping layer on the channel layer.
- Published
- 2019
16. Effect of carbon black addition on thermal stability and capacitive performances of supercapacitors
- Author
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Kyoungah Cho, Kyungwhan Yang, and Sangsig Kim
- Subjects
Materials science ,Oxide ,lcsh:Medicine ,02 engineering and technology ,Internal resistance ,010402 general chemistry ,01 natural sciences ,Capacitance ,Article ,law.invention ,chemistry.chemical_compound ,law ,Thermal stability ,lcsh:Science ,Supercapacitor ,Multidisciplinary ,Graphene ,lcsh:R ,Carbon black ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,Chemical engineering ,Electrode ,lcsh:Q ,0210 nano-technology - Abstract
In this study, we propose a simple way to improve thermal stability of solid-state supercapacitors (SCs) by adding carbon black (CB) into reduced graphene oxide (rGO) electrodes. The CB used as a heat-resistant additive contributes to stable operation of the rGO-CB SC even after 1000 charge/discharge cycles at 90 °C. In the case of the rGO SC without CB, it fails after the 166th cycles at 90 °C. Compared with the rGO SC, the rGO-CB SC exhibits the decrease in internal resistance from 42 to 18 Ω and the increase in specific capacitance from 115 to 160 F/g. Moreover, the rGO-CB SC shows a smaller variation in specific capacitance (12%) than that of rGO SC (30%) as the temperature increases from 30 to 90 °C. The observation reveals that the addition of CB being a heat-resistant additive helps improve performance of thermal stable SCs.
- Published
- 2018
17. Effect of Si on the Energy Band Gap Modulation and Performance of Silicon Indium Zinc Oxide Thin-Film Transistors
- Author
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Sungwoo Hwang, Kyung Sang Cho, Byeong Hyeon Lee, Jun Young Choi, Keun Heo, Sang Yeol Lee, Sangsig Kim, and JaeGwan Chung
- Subjects
010302 applied physics ,Multidisciplinary ,Materials science ,business.industry ,Band gap ,lcsh:R ,Doping ,lcsh:Medicine ,Fermi energy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Article ,Threshold voltage ,Amorphous solid ,Semiconductor ,Thin-film transistor ,0103 physical sciences ,Optoelectronics ,lcsh:Q ,Electrical measurements ,lcsh:Science ,0210 nano-technology ,business - Abstract
The band gap properties of amorphous SiInZnO (a-SIZO) thin-film transistors (TFTs) with different Si concentrations have been studied. The electronic structures of the films, engineered by controlling the Si content, have been investigated through the changes of the band gap and band edge states. Carrier generation at oxygen vacancies can modify the band gap states of oxide thin films. Si suppresses the number of oxygen vacancies—which are carrier generation sites—so shifts the Fermi energy level away from the conduction band. It is difficult to derive the electronic structures of amorphous oxide semiconductors by electrical measurements. Thus, we used a combination of ultraviolet photoelectron spectroscopy, Kelvin probe measurements, and electron energy loss spectroscopy to measure the band gap and electrical performance variations of SIZO TFTs with Si doping. To verify the versatility of Si doping in modulating electronic properties, high-performance depletion-mode inverter circuits consisting of 0.1 to 0.3 wt% Si-doped a-SIZO TFTs were fabricated. These inverter models operate through the threshold voltage difference that arises from the different Si contents. High voltage gains of ~20.62 at a supply voltage of 15 V were obtained with the two TFTs, with a strong dependence on the subthreshold swing.
- Published
- 2017
18. Engineering of band gap states of amorphous SiZnSnO semiconductor as a function of Si doping concentration
- Author
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Jun Young Choi, Sungwoo Hwang, Sang Yeol Lee, Sangsig Kim, Keun Heo, and Kyung Sang Cho
- Subjects
010302 applied physics ,Multidisciplinary ,Materials science ,business.industry ,Band gap ,Doping ,Fermi energy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Article ,Semimetal ,Amorphous solid ,Condensed Matter::Materials Science ,Semiconductor ,0103 physical sciences ,Optoelectronics ,Metal-induced gap states ,Direct and indirect band gaps ,0210 nano-technology ,business - Abstract
We investigated the band gap of SiZnSnO (SZTO) with different Si contents. Band gap engineering of SZTO is explained by the evolution of the electronic structure, such as changes in the band edge states and band gap. Using ultraviolet photoelectron spectroscopy (UPS), it was verified that Si atoms can modify the band gap of SZTO thin films. Carrier generation originating from oxygen vacancies can modify the band-gap states of oxide films with the addition of Si. Since it is not easy to directly derive changes in the band gap states of amorphous oxide semiconductors, no reports of the relationship between the Fermi energy level of oxide semiconductor and the device stability of oxide thin film transistors (TFTs) have been presented. The addition of Si can reduce the total density of trap states and change the band-gap properties. When 0.5 wt% Si was used to fabricate SZTO TFTs, they showed superior stability under negative bias temperature stress. We derived the band gap and Fermi energy level directly using data from UPS, Kelvin probe, and high-resolution electron energy loss spectroscopy analyses.
- Published
- 2016
19. Stable Bending Performance of Flexible Organic Light-Emitting Diodes Using IZO Anodes
- Author
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Kiyeol Kwak, Kyoungah Cho, and Sangsig Kim
- Subjects
Multidisciplinary ,Materials science ,Photoluminescence ,business.industry ,Exciton ,Thermionic emission ,Article ,Anode ,Amorphous solid ,PEDOT:PSS ,OLED ,Optoelectronics ,business ,Sheet resistance - Abstract
We report luminescent characteristics and mechanical stability of a flexible organic light-emitting diode (FOLED) using an amorphous ZnO-doped In2O3 (a-IZO) anode with a low sheet resistance of 18.9 Omega/square and a high optical transparency of 86%. The FOLED consisting of a-IZO/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT)/LiF/Al exhibits the efficient luminescent characteristics, which are nearly identical with the photoluminescence spectrum of the organic emitting material in our FOLED. This observation clearly indicates that the luminescent characteristics of the FOLED are solely ascribed to molecular exciton formation within the F8BT layer, since exciplex and charge transfer exciton formation are strictly suppressed by both tunneling/thermionic injection of holes at the PEDOT: PSS/F8BT interface and enhanced hole transport. Furthermore, the use of the considerably flexible a-IZO anode and PEDOT: PSS acting as a strain-relief buffering material enables good retention of the efficient luminescent characteristics of the FOLED even after continuous bending of up to 1000 times.
- Published
- 2013
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