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Jeon, Youngin,Kim, Minsuk,Kim, Yoonjoong,Kim, Sangsig American Chemical Society 2014 ACS NANO Vol.8 No.4
<P>In this study, we demonstrate the abruptly steep-switching characteristics of a feedback field-effect transistor (FBFET) with a channel consisting of a p<SUP><I>+</I></SUP><I>–</I>i<I>–</I>n<SUP><I>+</I></SUP> Si nanowire (NW) and charge spacers of discrete nanocrystals on a plastic substrate. The NW FBFET shows superior switching characteristics such as an on/off current ratio of ∼10<SUP>5</SUP> and an average subthreshold swing (SS) of 30.2 mV/dec at room temperature. Moreover, the average SS and threshold voltage values can be adjusted by programming. These sharp switching characteristics originate from a positive feedback loop generated by potential barriers in the intrinsic channel area. This paper describes in detail the switching mechanism of our device.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-4/nn500494a/production/images/medium/nn-2014-00494a_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn500494a'>ACS Electronic Supporting Info</A></P>
Flexible Nano-Floating-Gate Memory With Channels of Enhancement-Mode Si Nanowires
Youngin Jeon,Myeongwon Lee,Taeho Moon,Sangsig Kim IEEE 2012 IEEE transactions on electron devices Vol.59 No.11
<P>The electrical characteristics of a flexible nano-floating-gate memory (NFGM) device with a channel made of an enhancement-mode n<SUP>+</SUP>-p-n<SUP>+</SUP> Si nanowire (Si-NW) are investigated in this work. The NFGM based on the enhancement-mode Si-NW field-effect transistor is constructed on a plastic substrate with a Pt-nanocrystal floating-gate layer; it exhibits an on-current/off-current ratio of ~10<SUP>7</SUP> and a subthreshold swing of 88 mV/dec. The NFGM shows good memory characteristics and mechanical flexibility, such as a threshold voltage shift of 1.85 V, a retention time of up to ~10<SUP>4</SUP>s, and a stability for up to 1000 bending cycles. The present study demonstrates the promising potential of flexible Si-NW-based nonvolatile memories for future electronics.</P>
Jeon, Youngin,Kim, Minsuk,Lim, Doohyeok,Kim, Sangsig American Chemical Society 2015 NANO LETTERS Vol.15 No.8
<P>In this study, we present the steep switching characteristics of bendable feedback field-effect transistors (FBFETs) consisting of p(+)-i-n(+) Si nanowires (NWs) and dual-top-gate structures. As a result of a positive feedback loop in the intrinsic channel region, our FBFET features the outstanding switching characteristics of an on/off current ratio of approximately 106, and point subthreshold swings (SSs) of 18-19 mV/dec in the n-channel operation mode and of 10- 23 mV/dec in the p-channel operation mode. Not only can these devices operate in n- or p-channel modes, their switching characteristics can also be modulated by adjusting the gate biases. Moreover, the device maintains its steep SS characteristics, even when the substrate is bent. This study demonstrates the promising potential of bendable NW FBFETs for use as low-power components in integrated circuits or memory devices.</P>
Goh, Youngin,Ahn, Jaehan,Lee, Jeong Rak,Park, Wan Woo,Ko Park, Sang-Hee,Jeon, Sanghun American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.42
<P>Amorphous oxide semiconductor-based thin film transistors (TFTs) have been considered as excellent switching elements for driving active-matrix organic light-emitting diodes (AMOLED) owing to their high mobility and process compatibility. However, oxide semiconductors have inherent defects, causing fast transient charge trapping and device instability. For the next-generation displays such as flexible, wearable, or transparent displays, an active semiconductor layer with ultrahigh mobility and high reliability at low deposition temperature is required. Therefore, we introduced high density plasma microwave assisted (MWA) sputtering method as a promising deposition tool for the formation of high density and high-performance oxide semiconductor films. In this paper, we present the effect of the MWA sputtering method on the defects and fast charge trapping in In-Sn-Zn-O (ITZO) TFTs using various AC device characterization methodologies including fast I-V, pulsed I-V, transient current, low frequency noise, and discharge current analysis. Using these methods, we were able to analyze the charge trapping mechanism and intrinsic electrical characteristics, and extract the subgap density of the states of oxide TFTs quantitatively. In comparison to conventional sputtered ITZO, high density plasma MWA-sputtered ITZO exhibits outstanding electrical performance, negligible charge trapping characteristics and low subgap density of states. High-density plasma MWA sputtering method has high deposition rate even at low working pressure and control the ion bombardment energy, resulting in forming low defect generation in ITZO and presenting high performance ITZO TFT. We expect the proposed high density plasma sputtering method to be applicable to a wide range of oxide semiconductor device applications.</P>
Goh, Youngin,Jeon, Sanghun IOP 2018 Nanotechnology Vol.29 No.33
<P>Ferroelectric tunnel junctions (FTJs) have attracted research interest as promising candidates for non-destructive readout non-volatile memories. Unlike conventional perovskite FTJs, hafnia FTJs offer many advantages in terms of scalability and CMOS compatibility. However, so far, hafnia FTJs have shown poor endurance and relatively low resistance ratios and these have remained issues for real device applications. In our study, we fabricated HfZrO(HZO)-based FTJs with various electrodes (TiN, Si, SiGe, Ge) and improved the memory performance of HZO-based FTJs by using the asymmetry of the charge screening lengths of the electrodes. For the HZO-based FTJ with a Ge substrate, the effective barrier afforded by this FTJ can be electrically modulated because of the space charge-limited region formed at the ferroelectric/semiconductor interface. The optimized HZO-based FTJ with a Ge bottom electrode presents excellent ferroelectricity with a high remnant polarization of 18 <I>μ</I>C cm<SUP>−2</SUP>, high tunneling electroresistance value of 30, good retention at 85 °C and high endurance of 10<SUP>7</SUP>. The results demonstrate the great potential of HfO<SUB>2</SUB>-based FTJs in non-destructive readout non-volatile memories.</P>
Discharge Current Analysis Estimating the Defect Sites in Amorphous Hafnia Thin-Film Transistor
Goh, Youngin,Jeon, Sanghun Institute of Electrical and Electronics Engineers 2018 IEEE transactions on electron devices Vol.65 No.8
<P>Defects in amorphous oxide thin-film transistor (TFT) influence major transistor parameters such as the threshold voltage, mobility, and subthreshold slope. Thus, understanding these defects is crucial in securing high-reliability and high-performance devices. However, only very limited electrical analysis methods such as multifrequency <TEX>${C}$</TEX>– <TEX>${V}$</TEX> and temperature-dependent <TEX>${I}$</TEX>– <TEX>${V}$</TEX> methods have been applied to accumulation mode devices and these do not provide direct pictures of the defects during carrier transport. In this investigation, we employed the discharging current analysis method to attain quantitative information involving the defect densities of amorphous hafnium–indium–zinc–oxide (a-HIZO) TFT. We were able to estimate the number of defect sites of a-HIZO TFT as being of the order of 1018/cm<I><SUP>3</SUP></I>, although this is dependent on the Hf content. We believe that this method can be widely used to estimate the defect density of oxide TFTs.</P>
Goh, Youngin,Kim, Taeho,Yang, Jong-Heon,Choi, Ji Hun,Hwang, Chi-Sun,Cho, Sung Haeng,Jeon, Sanghun American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.11
<P>Active matrix organic light-emitting diodes (AMOLEDs) are considered to be a core component of next- generation display technology, which can he used for wearable and flexible devices. Reliable thin-film transistors (TFTs) with high mobility are required to drive AMOLEDs. Recently, amorphous oxide TFTs, due to their high mobility, have been considered as excellent substitutes for driving AMOLEDs. However, the device instabilities of high-mobility oxide TFTs 0 have remained a key issue to be used in production. In this paper, 0 we present the charge-trapping and device instability mechanisms of high-mobility oxide TFTs with double active layers, using In Zn-O (IZO) and Al-doped Sn-Zn-In-O (ATZIO) with various interfacial IZO thicknesses (0-6 nm). To this end, we employed microsecond fast current voltage (I-V), single-pulsed I-V, transient current, and discharge current analysis. These alternating-current device characterization methodologies enable the extraction of various trap parameters and defect densities as well as the understanding of dynamic charge transport in double-active-layer TFTs. The results show that the number of defect sites decreases with an increase in the interfacial IZO thickness. From these results, we conclude that the interfacial IZO layer plays a crucial role in minimizing charge trapping in ATZIO TFTs.</P>
Lim, Doohyeok,Jeon, Youngin,Kim, Minsuk,Kim, Yoonjoong,Kim, Sangsig American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.11
<P>Electrical characteristics of top-gate SnO2 thin-film transistors (TFTs) fabricated on bendable substrates using direct current reactive magnetron sputtering were examined in this study. A TFT with an n-type SnO2 channel film deposited with an oxygen partial pressure of 27% exhibits the best electrical performance. It had a field-effect mobility of 4.43 cm(2)/V . s and an on/off-current ratio of 4.19 x 10(6). This electrical performance is comparable and superior to n-type SnO2 TFTs previously reported by other research groups. The electrical characteristics of our SnO2 TFTs under tensile or compressive strain, and the recovery characteristics after bending stresses, will be discussed in this paper. This paper is the first report about the full functionality of n-type SnO2 TFTs on flexible substrates under bending stresses, to the best of our knowledge.</P>