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Lee, Junyeong,Park, Ji Hoon,Lee, Young Tack,Jeon, Pyo Jin,Lee, Hee Sung,Nam, Seung Hee,Yi, Yeonjin,Lee, Younjoo,Im, Seongil American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.7
<P>DNA-base small molecules of guanine, cytosine, adenine, and thymine construct the DNA double helix structure with hydrogen bonding, and they possess such a variety of intrinsic benefits as natural plentitude, biodegradability, biofunctionality, low cost, and low toxicity. On the basis of these advantages, here, we report on unprecedented useful applications of guanine layer as hydrogen getter and charge trapping layer when it is embedded into a dielectric oxide of n-channel inorganic InGaZnO and p-channel organic heptazole field effect transistors (FETs). The embedded guanine layer much improved the gate stability of inorganic FETs gettering many hydrogen atoms in the gate dielectric layer of FET, and it also played as charge trapping layer to which the voltage pulse-driven charges might be injected from channel, resulting in a threshold voltage (<I>V</I><SUB>th</SUB>) shift of FETs. Such shift state is very ambient-stable and almost irrevocable even under a high electric-field at room temperature. So, Boolean logics are nicely demonstrated by using our FETs with the guanine-embedded dielectric. The original <I>V</I><SUB>th</SUB> is recovered only under high energy blue photons by opposite voltage pulse (charge-ejection), which indicates that our device is also applicable to nonvolatile photo memory.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-7/am405998d/production/images/medium/am-2013-05998d_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am405998d'>ACS Electronic Supporting Info</A></P>
Single-Crystalline Silicon-Based Heterojunction Photodiode Arrays on Flexible Plastic Substrates
Sangwook Lee,Juree Hong,Ja Hoon Koo,Seulah Lee,Kwanghyun Lee,Seongil Im,Taeyoon Lee IEEE 2011 IEEE transactions on electron devices Vol.58 No.10
<P>A silicon-based photodiode array was fabricated on a flexible polyethylene terephthalate substrate using a transfer printing technique. A heterojunction structure composed of a 15-nm-thick highly doped hydrogenated amorphous-silicon (n<SUP>+</SUP> a-Si:H) layer and a 3-μm-thick p-type single-crystal silicon (p c-Si) membrane layer was adopted as the active layer of the flexible photodiode. The highly ordered photodiode array formed on the flexible substrate exhibited superior stability in electrical properties under bent conditions with no mechanical deformation. The variation of the spectral quantum efficiency (QE) under short-wavelength light illumination (λ ≤ 580 nm) was in excellent agreement with that of a heterojunction photodiode composed of a-Si:H and a bulk c-Si substrate. Relatively low QE values were observed under longer wavelength (λ ≥ 600 nm) illumination due to the finite thickness of the active layer. The <I>C</I>-<I>V</I> measurement results of the fabricated photodiode array were in accordance with the abrupt junction model. A closer inspection of the junction area of the device using high-resolution cross-sectional transmission micrograph exhibited an interface depth of 2 ± 0.5 nm, which is unavoidable in plasma-enhanced a-Si:H deposition processes.</P>
Lee, Kwang H.,Lee, Hee Sung,Lee, Kimoon,Ha, Taewoo,Kim, Jae Hoon,Im, Seongil WILEY‐VCH Verlag 2011 Advanced Materials Vol.23 No.10
<P><B>An almost transparent image pixel on glass</B> is demonstrated for the first time under visible and UV illumination at 3 V. The pixel is composed of a pentacene thin‐film transistor and a serially connected pentacene/ZnO photodiode, with or without a 6,13‐pentacenequinone phosphor layer that was deposited on the photodiode for more efficient light detection. </P>
Lee, Junyeong,Hwang, Hyuncheol,Min, Sung-Wook,Shin, Jae Min,Kim, Jin Sung,Jeon, Pyo Jin,Lee, Hee Sung,Im, Seongil American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.3
<P>Although organic field-effect transistors (OFETs) have various advantages of lightweight, low-cost, mechanical flexibility, and nowadays even higher mobility than amorphous Si-based FET, stability issue under bias and ambient condition critically hinder its practical application. One of the most detrimental effects on organic layer comes from penetrated atmospheric species such as oxygen and water. To solve such degradation problems, several molecular engineering tactics are introduced: forming a kinetic barrier, lowering the level of molecule orbitals, and increasing the band gap. However, direct passivation of organic channels, the most promising strategy, has not been reported as often as other methods. Here, we resolved the ambient stability issues of p-type (heptazole)/or n-type (PTCDI-C13) OFETs and their bias-stability issues at once, using DNA-base small molecule guanine (C<SUB>5</SUB>H<SUB>5</SUB>N<SUB>5</SUB>O)/Al<SUB>2</SUB>O<SUB>3</SUB> bilayer. The guanine protects the organic channels as buffer/and H getter layer between the channels and capping Al<SUB>2</SUB>O<SUB>3</SUB>, whereas the oxide capping resists ambient molecules. As a result, both p-type and n-type OFETs are simultaneously protected from gate-bias stress and 30 days-long ambient aging, finally demonstrating a highly stable, high-gain complementary-type logic inverter.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-3/am507354p/production/images/medium/am-2014-07354p_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am507354p'>ACS Electronic Supporting Info</A></P>
Low-voltage pentacene transistor inverters using micro-contact printed nano-layer
Lee, Kwang H.,Oh, Min Suk,Lee, Byoung H.,Sung, Myung M.,Im, Seongil Royal Society of Chemistry 2010 Journal of materials chemistry Vol.20 No.4
<P>We report on low-voltage inverters with two pentacene-based thin-film transistors (TFTs), one of which has been fabricated on a dielectric surface selected by micro-contact printing (μCP). When a self-assembled monolayer (SAM) of 7-octenyltrichlorosilane (7-OTS) was printed on AlO<SUB><I>x</I></SUB> dielectric oxide, the TFT with the μCP-SAM displayed a large threshold voltage (<I>V</I><SUB>th</SUB>) shift (3 V shift under −5 V operation), increased device current, and clearly changed pentacene surface morphology as compared to those of the other TFT without μCP-SAM. Those results are attributed to the 7-OTS-modified pentacene/AlO<SUB><I>x</I></SUB> interface. Our inverter, composed of two TFTs with and without μCP-SAM, shows a high gain of ∼50 at a supply voltage (<I>V</I><SUB>DD</SUB>) of −20 V.</P> <P>Graphic Abstract</P><P>Micro-contact printing of a hydrophobic nano-layer provides selective channel patterning for a pentacene organic inverter with two thin-film transistors (TFTs), of which the load-TFT is selected by the process, to control the inverter properties. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b922675c'> </P>
Lee, Byoung H,Lee, Kwang H,Im, Seongil,Sung, Myung M American Scientific Publishers 2009 Journal of Nanoscience and Nanotechnology Vol.9 No.12
<P>We report a vapor-phase molecular layer deposition (MLD) of self-assembled multilayer thin films for organic thin-film transistor. In the present MLD process, alkylsiloxane self-assembled multilayers (SAMs) were grown under vacuum by repeated sequential adsorptions of C=C-terminated alkylsilane and aluminum hydroxide with ozone activation. The MLD method is a self-controlled layer-by-layer growth process, and is perfectly compatible with the atomic layer deposition (ALD) method. The SAMs films prepared exhibited good mechanical flexibility and stability, excellent insulating properties, and relatively high dielectric capacitances of 374 nF/cm2 with a high dielectric strength of 4 MV/cm. They were then used as a 12 nm-thick dielectric for pentacene-based thin-film transistors (TFTs), which showed a maximum field effect mobility of 0.57 cm2/V s, operating at -4 V with an on/off current ratio of approximately 10(3).</P>
Lee, Kimoon,Lee, Byoung H.,Lee, Kwang H.,Park, Ji Hoon,Sung, Myung M.,Im, Seongil Royal Society of Chemistry 2010 Journal of materials chemistry Vol.20 No.13
<P>We report on photo-excited trap-charge-collection spectroscopy as a direct probe of the traps in organic field-effect transistors (OFETs). Monochromatic photon beams transmitted through the working channels of 5 V operating pentacene-OFETs with 60 nm thick Al<SUB>2</SUB>O<SUB>3</SUB> dielectrics liberate interface charges trapped at the matched energy level while the oxide surfaces were prepared with various self-assembled monolayers (SAMs). The density of states (DOS) of traps is directly mapped as a function of the photon energy by tracking the change in the threshold voltage. While conventional electrical stability measurements qualitatively support our trap DOS spectroscopy results, our direct measurement technique provides a powerful tool for quantitative analysis of the nature and density of interfacial traps in field-effect transistor devices.</P> <P>Graphic Abstract</P><P>Direct quantitative analysis, named the photo-excited charge-collection technique, for the interface traps at the pentacene OFET channel was implemented by using monochromatic photons which are carried by optical fibers and are probed in OFETs. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b921636g'> </P>
Lee, Kwang H.,Lee, Gyubaek,Lee, Kimoon,Oh, Min Suk,Im, Seongil,Yoon, Sung-Min WILEY-VCH Verlag 2009 Advanced Materials Vol.21 No.42
<B>Graphic Abstract</B> <P>Nonvolatile memory ferroelectric thin-film transistors (FeTFT) with P(VDF-TrFE) polymer are demonstrated with both n-channel ZnO and p-channel pentacene. A high mobility of ≈1 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> and large memory window of ≈20 V are achieved through the organic ferroelectric– inorganic channel hybrid device of ZnO-FeTFT. WRITE/ERASE states are clearly distinguished by ±20 V switching for ZnO- and pentacene-FeTFTs. <img src='wiley_img/09359648-2009-21-42-ADMA200900398-content.gif' alt='wiley_img/09359648-2009-21-42-ADMA200900398-content'> </P>
Lee, Young Tack,Kwon, Hyeokjae,Kim, Jin Sung,Kim, Hong-Hee,Lee, Yun Jae,Lim, Jung Ah,Song, Yong-Won,Yi, Yeonjin,Choi, Won-Kook,Hwang, Do Kyung,Im, Seongil American Chemical Society 2015 ACS NANO Vol.9 No.10
<P>Two-dimensional van der Waals (2D vdWs) materials are a class of new materials that can provide important resources for future electronics and materials sciences due to their unique physical properties. Among 2D vdWs materials, black phosphorus (BP) has exhibited significant potential for use in electronic and optoelectronic applications because of its allotropic properties, high mobility, and direct and narrow band gap. Here, we demonstrate a few-layered BP-based nonvolatile memory transistor with a poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) ferroelectric top gate insulator. Experiments showed that our BP-based ferroelectric transistors operate satisfactorily at room temperature in ambient air and exhibit a clear memory window. Unlike conventional ambipolar BP transistors, our ferroelectric transistors showed only p-type characteristics due to the carbon–fluorine (C–F) dipole effect of the P(VDF-TrFE) layer, as well as the highest linear mobility value of 1159 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP> with a 10<SUP>3</SUP> on/off current ratio. For more advanced memory applications beyond unit memory devices, we implemented two memory inverter circuits, a resistive-load inverter circuit and a complementary inverter circuit, combined with an n-type molybdenum disulfide (MoS<SUB>2</SUB>) nanosheet. Our memory inverter circuits displayed a clear memory window of 15 V and memory output voltage efficiency of 95%.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-10/acsnano.5b04592/production/images/medium/nn-2015-04592m_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b04592'>ACS Electronic Supporting Info</A></P>