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Threshold Voltage (threshold + voltage)
Terms modified by Threshold Voltage Selected AbstractsControllable Shifts in Threshold Voltage of Top-Gate Polymer Field-Effect Transistors for Applications in Organic Nano Floating Gate MemoryADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Kang-Jun Baeg Abstract Organic field-effect transistor (FET) memory is an emerging technology with the potential to realize light-weight, low-cost, flexible charge storage media. Here, solution-processed poly[9,9-dioctylfluorenyl-2,7-diyl]-co-(bithiophene)] (F8T2) nano floating gate memory (NFGM) with a top-gate/bottom-contact device configuration is reported. A reversible shift in the threshold voltage (VTh) and reliable memory characteristics was achieved by the incorporation of thin Au nanoparticles (NPs) as charge storage sites for negative charges (electrons) at the interface between polystyrene and cross-linked poly(4-vinylphenol). The F8T2 NFGM showed relatively high field-effect mobility (µFET) (0.02,cm2 V,1 s,1) for an amorphous semiconducting polymer with a large memory window (ca. 30,V), a high on/off ratio (more than 104) during writing and erasing with an operation voltage of 80,V of gate bias in a relatively short timescale (less than 1,s), and a retention time of a few hours. This top-gated polymer NFGM could be used as an organic transistor memory element for organic flash memory. [source] Development of ionic currents of zebrafish slow and fast skeletal muscle fibersDEVELOPMENTAL NEUROBIOLOGY, Issue 3 2006Christopher A. Coutts Abstract Voltage-gated Na+ and K+ channels play key roles in the excitability of skeletal muscle fibers. In this study we investigated the steady-state and kinetic properties of voltage-gated Na+ and K+ currents of slow and fast skeletal muscle fibers in zebrafish ranging in age from 1 day postfertilization (dpf) to 4,6 dpf. The inner white (fast) fibers possess an A-type inactivating K+ current that increases in peak current density and accelerates its rise and decay times during development. As the muscle matured, the V50s of activation and inactivation of the A-type current became more depolarized, and then hyperpolarized again in older animals. The activation kinetics of the delayed outward K+ current in red (slow) fibers accelerated within the first week of development. The tail currents of the outward K+ currents were too small to allow an accurate determination of the V50s of activation. Red fibers did not show any evidence of inward Na+ currents; however, white fibers expressed Na+ currents that increased their peak current density, accelerated their inactivation kinetics, and hyperpolarized their V50 of inactivation during development. The action potentials of white fibers exhibited significant changes in the threshold voltage and the half width. These findings indicate that there are significant differences in the ionic current profiles between the red and white fibers and that a number of changes occur in the steady-state and kinetic properties of Na+ and K+ currents of developing zebrafish skeletal muscle fibers, with the most dramatic changes occurring around the end of the first day following egg fertilization. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2006 [source] Dual-Gate Organic Field-Effect Transistors as Potentiometric Sensors in Aqueous SolutionADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Mark-Jan Spijkman Abstract Buried electrodes and protection of the semiconductor with a thin passivation layer are used to yield dual-gate organic transducers. The process technology is scaled up to 150-mm wafers. The transducers are potentiometric sensors where the detection relies on measuring a shift in the threshold voltage caused by changes in the electrochemical potential at the second gate dielectric. Analytes can only be detected within the Debye screening length. The mechanism is assessed by pH measurements. The threshold voltage shift depends on pH as ,Vth,=,(Ctop/Cbottom),×,58,mV per pH unit, indicating that the sensitivity can be enhanced with respect to conventional ion-sensitive field-effect transistors (ISFETs) by adjusting the ratio of the top and bottom gate capacitances. Remaining challenges and opportunities are discussed. [source] Improving the ON/OFF Ratio and Reversibility of Recording by Rational Structural Arrangement of Donor,Acceptor MoleculesADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Ying Ma Abstract Organic molecules with donor,acceptor (D,A) structure are an important type of material for nanoelectronics and molecular electronics. The influence of the electron donor and acceptor units on the electrical function of materials is a worthy topic for the development of high-performance data storage. In this work, the effect of different D,A structures (namely D,,,A,,,D and A,,,D,,,A) on the electronic switching properties of triphenylamine-based molecules is investigated. Devices based on D,,,A,,,D molecules exhibit excellent write,read,erase characteristics with a high ON/OFF ratio of up to 106, while that based on A,,,D,,,A molecules exhibit irreversible switching behavior with an ON/OFF ratio of about (3.2,×,101),(1,×,103). Moreover, long retention time of the high conductance state and low threshold voltage are observed for the D,A switching materials. Accordingly, stable and reliable nanoscale data storage is achieved on the thin films of the D,A molecules by scanning tunneling microscopy. The influence of the arrangement of the D and A within the molecular backbone disclosed in this study will be of significance for improving the electronic switching properties (ON/OFF current ratio and reversibility) of new molecular systems, so as to achieve more efficient data storage through appropriate design strategies. [source] Printed Sub-2 V Gel-Electrolyte-Gated Polymer Transistors and CircuitsADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Yu Xia Abstract The fabrication and characterization of printed ion-gel-gated poly(3-hexylthiophene) (P3HT) transistors and integrated circuits is reported, with emphasis on demonstrating both function and performance at supply voltages below 2,V. The key to achieving fast sub-2,V operation is an unusual gel electrolyte based on an ionic liquid and a gelating block copolymer. This gel electrolyte serves as the gate dielectric and has both a short polarization response time (<1,ms) and a large specific capacitance (>10,µF cm,2), which leads simultaneously to high output conductance (>2,mS mm,1), low threshold voltage (<1,V) and high inverter switching frequencies (1,10,kHz). Aerosol-jet-printed inverters, ring oscillators, NAND gates, and flip-flop circuits are demonstrated. The five-stage ring oscillator operates at frequencies up to 150,Hz, corresponding to a propagation delay of 0.7 ms per stage. These printed gel electrolyte gated circuits compare favorably with other reported printed circuits that often require much larger operating voltages. Materials factors influencing the performance of the devices are discussed. [source] Controllable Shifts in Threshold Voltage of Top-Gate Polymer Field-Effect Transistors for Applications in Organic Nano Floating Gate MemoryADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Kang-Jun Baeg Abstract Organic field-effect transistor (FET) memory is an emerging technology with the potential to realize light-weight, low-cost, flexible charge storage media. Here, solution-processed poly[9,9-dioctylfluorenyl-2,7-diyl]-co-(bithiophene)] (F8T2) nano floating gate memory (NFGM) with a top-gate/bottom-contact device configuration is reported. A reversible shift in the threshold voltage (VTh) and reliable memory characteristics was achieved by the incorporation of thin Au nanoparticles (NPs) as charge storage sites for negative charges (electrons) at the interface between polystyrene and cross-linked poly(4-vinylphenol). The F8T2 NFGM showed relatively high field-effect mobility (µFET) (0.02,cm2 V,1 s,1) for an amorphous semiconducting polymer with a large memory window (ca. 30,V), a high on/off ratio (more than 104) during writing and erasing with an operation voltage of 80,V of gate bias in a relatively short timescale (less than 1,s), and a retention time of a few hours. This top-gated polymer NFGM could be used as an organic transistor memory element for organic flash memory. [source] Variable Temperature Mobility Analysis of n-Channel, p-Channel, and Ambipolar Organic Field-Effect TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Joseph A. Letizia Abstract The temperature dependence of field-effect transistor (FET) mobility is analyzed for a series of n-channel, p-channel, and ambipolar organic semiconductor-based FETs selected for varied semiconductor structural and device characteristics. The materials (and dominant carrier type) studied are 5,5,,,-bis(perfluorophenacyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (1, n-channel), 5,5,,,-bis(perfluorohexyl carbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (2, n-channel), pentacene (3, p-channel); 5,5,,,-bis(hexylcarbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (4, ambipolar), 5,5,,,-bis-(phenacyl)-2,2,: 5,,2,:5,,2,,,-quaterthiophene (5, p-channel), 2,7-bis((5-perfluorophenacyl)thiophen-2-yl)-9,10-phenanthrenequinone (6, n-channel), and poly(N -(2-octyldodecyl)-2,2,-bithiophene-3,3,-dicarboximide) (7, n-channel). Fits of the effective field-effect mobility (µeff) data assuming a discrete trap energy within a multiple trapping and release (MTR) model reveal low activation energies (EAs) for high-mobility semiconductors 1,3 of 21, 22, and 30,meV, respectively. Higher EA values of 40,70,meV are exhibited by 4,7 -derived FETs having lower mobilities (µeff). Analysis of these data reveals little correlation between the conduction state energy level and EA, while there is an inverse relationship between EA and µeff. The first variable-temperature study of an ambipolar organic FET reveals that although n-channel behavior exhibits EA,=,27,meV, the p-channel regime exhibits significantly more trapping with EA,=,250,meV. Interestingly, calculated free carrier mobilities (µ0) are in the range of ,0.2,0.8,cm2,V,1 s,1 in this materials set, largely independent of µeff. This indicates that in the absence of charge traps, the inherent magnitude of carrier mobility is comparable for each of these materials. Finally, the effect of temperature on threshold voltage (VT) reveals two distinct trapping regimes, with the change in trapped charge exhibiting a striking correlation with room temperature µeff. The observation that EA is independent of conduction state energy, and that changes in trapped charge with temperature correlate with room temperature µeff, support the applicability of trap-limited mobility models such as a MTR mechanism to this materials set. [source] A New Carbazole-Constructed Hyperbranched Polymer: Convenient One-Pot Synthesis, Hole-Transporting Ability, and Field-Effect Transistor PropertiesADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Zhong'an Li Abstract A new hyperbranched polymer (HB-car), constructed fully by carbazole moieties, is successfully synthesized through a one-pot Suzuki coupling reaction. The resultant polymer is well-characterized, and its hole-transporting ability is studied carefully. The device, in which HB-car is utilized as a hole-transporting layer and tris-(8-hydroxyquinoline) aluminum as an electron-emitting layer as well as electron-transporting layer, gives a much higher efficiency (3.05,cd A,1), than that of a poly(N -vinylcarbazole) based device (2.19,cd A,1) under similar experimental conditions. The remarkable performance is attributed to its low energy barrier and enhanced hole-drifting ability in the HB-car based device. In addition, for the first time, a field-effect transistor (FET) based on the hyperbranched polymer is fabricated, and the organic FET device shows that HB-car is a typical p -type FET material with a saturation mobility of 1,×,10,5,cm2 V,1 s,1, a threshold voltage of ,47.1,V, and an on-to-off current ratio of 103. [source] Threshold Voltage Shifts in Organic Thin-Film Transistors Due to Self-Assembled Monolayers at the Dielectric SurfaceADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Stefan K. Possanner Abstract Recently, it has been shown by several groups that the electrical characteristics of organic thin-film transistors (OTFTs) can be significantly influenced by depositing self-assembled monolayers (SAMs) at the organic semiconductor/dielectric interface. In this work, the effect of such SAMs on the transfer characteristics and especially on the threshold voltage of OTFTs is investigated by means of two-dimensional drift-diffusion simulations. The impact of the SAM is modeled either by a permanent space charge layer that can result from chemical reactions with the active material, or by a dipole layer representing an array of ordered dipolar molecules. It is demonstrated that, in both model cases, the presence of the SAM significantly changes the transfer characteristics. In particular, it gives rise to a modified, effective gate voltage Veff that results in a rigid shift of the threshold voltage, ,Vth, relative to a SAM-free OTFT. The achievable amount of threshold voltage shift, however, strongly depends on the actual role of the SAM. While for the investigated device dimensions, an organic SAM acting as a dipole layer can realistically shift the threshold voltage only by a few volts, the changes in the threshold voltage can be more than an order of magnitude larger when the SAM leads to charges at the interface. Based on the analysis of the different cases, a route to experimentally discriminate between SAM-induced space charges and interface dipoles is proposed. The developed model allows for qualitative description of the behavior of organic transistors containing reactive interfacial layers; when incorporating rechargeable carrier trap states and a carrier density-dependent mobility, even a quantitative agreement between theory and recent experiments can be achieved. [source] Enhancement of Carrier Mobilities of Organic Semiconductors on Sol,Gel Dielectrics: Investigations of Molecular Organization and Interfacial Chemistry EffectsADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Tommy Cahyadi Abstract The dielectric-semiconductor interfacial interactions critically influence the morphology and molecular ordering of the organic semiconductor molecules, and hence have a profound influence on mobility, threshold voltage, and other vital device characteristics of organic field-effect transistors. In this study, p-channel small molecule/polymer (evaporated pentacene and spin-coated poly(3,3,;-didodecylquarterthiophene) , PQT) and n-channel fullerene derivative ({6}-1-(3-(2-thienylethoxycarbonyl)-propyl)-{5}-1-phenyl-[5,6]-C61 , TEPP-C61) show a significant enhancement in device mobilities ranging from ,6 to ,45 times higher for all classes of semiconductors deposited on sol,gel silica gate-dielectric than on pristine/octyltrichlorosilane (OTS)-treated thermally grown silica. Atomic force microscopy, synchrotron X-ray diffraction, photoluminescence/absorption, and Raman spectroscopy studies provide comprehensive evidences that sol,gel silica dielectrics-induced enhancement in both p- and n-channel organic semiconductors is attributable to better molecular ordering/packing, and hence reduced charge trapping centers due to lesser structural defects at the dielectric-semiconductor interface. [source] Extracting Parameters from the Current,Voltage Characteristics of Organic Field-Effect TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 11 2004G. Horowitz Abstract Organic field-effect transistors were fabricated with vapor-deposited pentacene on aluminum oxide insulating layers. Several methods are used in order to extract the mobility and threshold voltage from the transfer characteristic of the devices. In all cases, the mobility is found to depend on the gate voltage. The first method consists of deriving the drain current as a function of gate voltage (transconductance), leading to the so-called field-effect mobility. In the second method, we assume a power-law dependence of the mobility with gate voltage together with a constant contact resistance. The third method is the so-called transfer line method, in which several devices with various channel length are used. It is shown that the mobility is significantly enhanced by modifying the aluminum oxide layer with carboxylic acid self-assembled monolayers prior to pentacene deposition. The methods used to extract parameters yield threshold voltages with an absolute value of less than 2 V. It is also shown that there is a shift of the threshold voltage after modification of the aluminum oxide layer. These features seem to confirm the validity of the parameter-extraction methods. [source] Nanoparticle-Dispersed Liquid Crystals Fabricated by Sputter DopingADVANCED MATERIALS, Issue 5 2010Hiroyuki Yoshida A simple and robust method to prepare nanoparticle-dispersed liquid crystals is demonstrated. Highly dispersed gold nanoparticle,liquid crystal suspensions are fabricated by simply sputter doping the gold target on the host liquid crystal (see figure). The existence of the nanoparticles is supported by optical extinction measurements, polarization optical microscopy, and transmission electron microscopy. An improvement in the electro-optic response, namely, a decrease in the threshold voltage, is also demonstrated in twist nematic devices fabricated using the nanoparticle-dispersed liquid crystal. [source] Flexible Fullerene Field-Effect Transistors Fabricated Through Solution ProcessingADVANCED MATERIALS, Issue 47 2009Chao-Feng Sung C60-based thin-film transistors are fabricated through solution processing. On rigid indium tin oxide glass, the transistors display electron mobilities as high as 0.21,cm2 V,1 s,1 and a threshold voltage of 0.7,V, only slightly lower than those of organic thin-film transistors prepared through vacuum deposition. On ITO-coated PET substrates, the mobilities in the flexible devices (see image) are approximately one order of magnitude lower than those of devices prepared on rigid glass substrates. [source] Energy Harvesting Using Piezoelectric Nanowires,A Correspondence on "Energy Harvesting Using Nanowires?"ADVANCED MATERIALS, Issue 13 2009by Alexe et al. A response to the questions raised by Alexe et al. concerning nanowire-based nanogenerators is presented. Evidence is given about the existence and detection of a piezoelectric potential in ZnO nanowires. The role played by the piezoelectric potential is to overcome the threshold voltage at the Pt,ZnO junction, while the observed output signal of ,10,mV is the difference in Fermi levels between the two electrodes. The measurement system used by Alexe et al. is questioned, as is their model. [source] Analysis and optimization of a novel biasing for constant-gain CMOS open-loop amplifiersINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 3 2001G. Palmisano A replica biasing circuit is presented which allows open-loop gain in CMOS amplifiers to be accurately set. The proposed solution is a new biasing which takes advantage of a triode-biased transistor instead of the ,VGS approach which is the traditional one. The circuit can be applied to both RF and IF amplifiers which are based on resistive loads in order to achieve high-frequency and/or low-noise performance. A detailed analysis of second-order effects is then given which emphasizes the effects due to mobility degradation, channel-length modulation and threshold voltage mismatches. Simulated results show a good sensitivity to process variations. Copyright © 2001 John Wiley & Sons, Ltd. [source] Investigation of multi-layered-gate electrode workfunction engineered recessed channel (MLGEWE-RC) sub-50,nm MOSFET: A novel designINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 3 2009Rishu Chaujar Abstract In this paper, a two-dimensional (2D) analytical sub-threshold model for a novel sub-50,nm multi-layered-gate electrode workfunction engineered recessed channel (MLGEWE-RC) MOSFET is presented and investigated using ATLAS device simulator to counteract the large gate leakage current and increased standby power consumption that arise due to continued scaling of SiO2 -based gate dielectrics. The model includes the evaluation of surface potential, electric field along the channel, threshold voltage, drain-induced barrier lowering, sub-threshold drain current and sub-threshold swing. Results reveal that MLGEWE-RC MOSFET design exhibits significant enhancement in terms of improved hot carrier effect immunity, carrier transport efficiency and reduced short channel effects proving its efficacy for high-speed integration circuits and analog design. Copyright © 2008 John Wiley & Sons, Ltd. [source] Preparation and characterization of PDLC films formed using a two-step procedureADVANCES IN POLYMER TECHNOLOGY, Issue 1 2007Yu-Che Hsiao Abstract A novel polymer-dispersed liquid crystal composite film was prepared using liquid crystal and dual resins, namely, UV-curable urethane diacrylate and thermo-curable epoxy, with a fixed LC content of 50 wt%. A combination treatment of UV irradiation and heat was performed in sequential steps. At first, the urethane diacrylate resin was cross-linked through UV irradiation and a pre-UV-cured film was formed. Then, the pre-UV-cured film was heat treated for curing the thermo-curable epoxy resin. As the thermal polymerization continued, LC droplets were formed and became embedded within the polymer matrix. PDLC films obtained from the polymer matrix with refractive indices in a range from 1.511 to 1.523 (1.517 ± 0.006) have optimal electro-optical properties. Films with a refractive index higher than 1.523 have high contrast ratio (CR), threshold voltage (Vth), and V90, whereas those with a low refractive index of 1.508 have low CR, Vth, and V90. In this study, we found that PDLC composite films with optimal compositions prepared by dual resins (UV/thermal) have good electro-optical properties. © 2007 Wiley Periodicals, Inc. Adv Polym Techn 26:14,20, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20087 [source] Immiscible polymers in double spin-coated electroluminescent devices containing phenyl-substituted tris(8-hydroxyquinoline)aluminum derivatives soluble in a host polymerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2003E. Shoji Abstract Three new phenyl-substituted tris(8-hydroxyquinoline)aluminum (AlQ3) derivatives have been synthesized: tris(5-phenyl-8-quinolinolate-N1,O8)aluminum, tris(5,7-diphenyl-8-quinolinolate-N1,O8)aluminum, and tris[5,7-bis(p -fluorophenyl)-8-quinolinolate-N1,O8]aluminum. These AlQ3 derivatives are easily soluble in common organic solvents and form solid-phase solutions in a poly(aryl ether ketone) host polymer (A435). These interesting properties allow the use of soluble AlQ3 derivatives in double spin-coated organic light-emitting devices of the type ITO/NPB-QP/A435 + 50 wt % soluble AlQ3 derivative/Mg, where NPB-QP is a hole-transporting polymer insoluble in toluene, the solvent for A435. Typical double spin-coated organic layer devices are characterized by an emission at 530,539 nm, a threshold voltage of 6,9 V, and a maximum luminance of 1800,4000 cd/m2 at 21,25 V. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3006,3016, 2003 [source] A bandwidth-compensated transimpedance amplifier for multigigabit optical receiversMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2001F. Centurelli Abstract In this paper, a transimpedance amplifier with an automatic bandwidth compensation circuit is presented. The proposed topology includes a transimpedance amplifier which features a bandwidth control input, and a replica bias circuit to sense the active device dc parameter variations. A Monte Carlo analysis shows a 140 MHz bandwidth variation around 8.1 GHz when a ±50% variation is considered for the transconductance and threshold voltage of the HEMT devices. The same simulation shows a 490 MHz bandwidth variation if the compensation circuit is removed. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 79,81, 2001. [source] HfO2/AlGaN/GaN structures with HfO2 deposited at ultra low pressure using an e-beamPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 5 2007V. Tokranov Abstract We show that HfO2/AlGaN/GaN structures with HfO2 layer deposited using an e-beam in ultra high vacuum are suitable for field effect transistors. The dielectric constant of the HfO2 was found ,HfO > 23,24, which is close to the highest re- ported values for this material. The leakage current did not exceed 10,4 A/cm2 at the threshold voltage. The comparison of the losses in the samples with and without HfO2 indicates low concentration of the interface traps. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] InGaN-based 518 and 488,nm laser diodes on c -plane GaN substratePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2010Takashi Miyoshi Abstract We succeeded in fabricating InGaN-based laser diodes (LDs) with a wavelength of 518 and 488,nm under continuous wave (cw) operation. The both LDs structures were grown on conventional c -plane GaN substrates by metal organic chemical vapor deposition (MOCVD). The threshold current and threshold voltage were 45,mA and 5.5,V at 518,nm, 30,mA and 4.5,V at 488,nm, respectively. The lifetime test of these LDs was carried out under high driving temperature up to 80,°C in cw operation. Lifetime was estimated to be over 5000,h with an optical output power of 5,mW at 80,°C in 515,518,nm LDs from 1000,h operation, and was estimated to be over 10,000,h with an output power of 60,mW at 60,°C in 488,nm LDs from 2000,h operation. [source] Influence of top layer geometries on the electronic properties of pentacene and diindenoperylene thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2008M. Scharnberg Abstract Top layers have a pronounced influence on the electronic properties of molecular organic thin films. Here, we report about the changes induced by metallic and polymeric top layers and contacts. As test structures, model systems of diindenoperylene and pentacene crystalline molecular organic thin films are used. A very sensitive radiotracer technique is introduced to study the details of metal penetration during top contact formation. The influence of temperature, evaporation time, adhesion promoter and grain size of the organic film were examined. The electric currents passing through metal top contacts were found to vary by more than a factor of three, depending on the preparation conditions of the metal contact. Furthermore, the series resistance of chemically identical contacts that only differed in the morphology of the interface were found to show pronounced asymmetric conductivity behaviour. We also show that with the help of electret top layers, based on the Teflon-AF fluropolymer, the threshold voltage of an organic field effect transistor can be tuned by several volts. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Integration of enhancement and depletion-mode AlGaN/GaN MIS-HFETs by fluoride-based plasma treatmentPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2007Ruonan Wang Abstract Enhancement-mode AlGaN/GaN metal,insulator,semiconductor HFETs (MIS-HFETs) are demonstrated by combining CF4 plasma treatment technique and a two-step Si3N4 deposition process. The threshold voltage has been shifted from ,4 to 2 V using this technique. A 15 nm Si3N4 layer is inserted under the gate to provide additional isolation between the gate metal and AlGaN surface, which can lead to higher gate turn-on voltage. The two-step Si3N4 deposition process is developed to reduce the gate coupling capacitances in the source and drain access regions, while assuring the plasma-treated gate region being fully covered by the gate electrode. The forward gate turn-on voltage can be as large as 6.8 V. By tuning the plasma treatment parameters, the threshold voltage of the enhancement-mode MIS-HFETs can be raised to as high as 4.3 V. By integrating with depletion-mode MIS-HFETs, a direct-coupled FET logic inverter has been fabricated, with logic low and high noise margins of 2.1 and 2 V. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Strain-engineered novel III,N electronic devices with high quality dielectric/semiconductor interfacesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003M. Asif Khan Abstract Since the early demonstration of 2D-electron gas [M. A. Khan et al., Appl. Phys. Lett. 60, 3027 (1992)] and a heterojunction field effect transistor (HFET) [M. Asif Khan et al., Appl. Phys. Lett. 63, 1214 (1993)] in III,N materials, rapid progress has been made to improve the DC and RF performance of GaN,AlGaN based HFETs. Stable and impressive microwave powers as high as 4,8 W/mm have been reported for device operation frequencies from 10 to 35 GHz. The key reason for these high performance numbers is an extremely large sheet carrier densities (>1 × 1013 cm,2) that can be induced at the interfaces in III,N hetereojunction [A. Bykhovsk et al., J. Appl. Phys. 74, 6734 (1993); M. Asif Khan et al., Appl. Phys. Lett. 75, 2806 (1999)]. These are instrumental in screening the channel dislocations thereby retaining large room temperature carrier mobilities (>1500 cm2/Vs) and sheet resistance as low as 300 ,/sq. These numbers and the high breakdown voltages of the large bandgap III,N material system thus enable rf-power approximately 5,10 times of that possible with GaAs and other competitor's technologies. We have recently introduced a unique pulsed atomic layer epitaxy approach to deposit AlN buffer layers and AlN/AlGaN superlattices [J. Zhang et al., Appl. Phys. Lett. 79, 925 (2001); J. P. Zhang et al., Appl. Phys. Lett. 80, 3542 (2002)] to manage strain and decrease the dislocation densities in high Al-content III,N layers. This has enabled us to significantly improve GaN/AlGaN hetereojunctions and the device isolation. The resulting low defect layers are not only key to improving the electronic but also deep ultraviolet light-emitting diode devices. For deep UV LED's they enabled us to obtain peak optical powers as high as 10 mW and 3 mW for wavelengths as short as 320 nm and 278 nm. Building on our past work [M. Asif Khan et al., Appl. Phys. Lett. 77, 1339 (2000); X. Hu et al., Appl. Phys. Lett. 79, 2832 (2001)] we have now deposited high quality SiO2/Si3N4 films over AlGaN with low interface state densities. They have then been used to demonstrate III,N insulating gate transistors (MOSHFET (SiO2) and MISHFET (Si3N4) with gate leakage currents 4,6 order less than those for conventional GaN,AlGaN HFETs. The introduction of the thin insulator layers (less then 100 Å) under the gate increases the threshold voltage by 2,3 V. In addition, it reduces the peak transconductance gm. However the unity cut-off frequency, the gain and the rf-powers remain unaffected as the gm/Cgs (gate-source capacitance) ratio remains unchanged. In addition to managing the defects and gate leakage currents we have also employed InGaN channel double heterojunction structures (AlInGaN,InGaN,GaN) to confine the carriers thereby reducing the spillover into trappings states. These InGaN based MOS-DHFETs exhibited no current-collapse, extremely low gate leakage currents (<10,10 A/mm) and 10,26 GHz rf-powers in excess of 6 W/mm. We have also demonstrated the scalability and stable operation of our new and innovative InGaN based insulating gate heterojunction field effect transistor approach. In this paper we will review the III,N heterojunction field-effect transistors progress and pioneering innovations including the excellent work from several research groups around the world. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Normally-on/off AlN/GaN high electron mobility transistorsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010C. Y. Chang Abstract We report on the novel normally-on/off AlN/GaN high electron mobility transistors (HEMTs) grown by plasma-assisted molecular beam epitaxy. With simple oxygen exposure, the threshold voltage can be tuned from -2.76 V to +1.13 V depending on the treatment time. The gate current was reduced and current-voltage curves show metal-oxide semiconductor diode-like characteristics after oxygen plasma exposure. The extrinsic transconductance of HEMTs decrease with increasing oxygen plasma exposure time due to the thicker Al oxide formed on the gate area. The unity current gain cut-off frequency, fT, and maximum frequency of oscillation, fmax, were 20.4 GHz and 36.5 GHz, respectively for an enhancement-mode HEMT with the gate dimension of 0.4 × 100 ,m2. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature dependence of normally off mode AlGaN/GaN heterostructure field-effect transistors with p-GaN gatePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010Takayuki Sugiyama Abstract We demonstrated high-temperature operation of normally off-mode junction-heterostructure-field-effect transistors (JHFETs) with a p-GaN gate that shows a very small shift of the threshold voltage against ambient temperature. Distinct normally off-mode operation with a maximum drain current of 93.2 mA/mm at 300 °C was realized. Therefore, normally off-mode GaN-based JFETs are greatly superior to Si-based devices as high-temperature switching devices. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of barrier thickness on AlInN/AlN/GaN heterostructures and device propertiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009H. Behmenburg Abstract We report on structural and device properties of AlInN/AlN/GaN transistor heterostructures grown by metal organic vapour phase epitaxy (MOVPE) on 2, sapphire substrates with AlInN barriers of thicknesses between 4 nm and 10 nm. The In content and thickness of the thin AlInN barrier is shown to be well determinable by high-resolution X-ray diffraction (HRXRD). Room temperature Hall measurements yielded similar mobility between 1400 cm2V,1s,1 and 1520 cm2V,1s,1 on all samples and increasing sheet carrier concentration ns with rising barrier thickness resulting in a minimum sheet resistance value of 200 Ohm/,. The effect of surface passivation with Si3N4 on the electrical properties is investigated and found to strongly increase sheet carrier concentration ns of the two-dimensional electron gas (2DEG) to values above 2×1013cm,2. Characterization of transistors with gate length Lg of 1.5 ,m produced from the grown samples reveals high transconductance (gm) and a maximum drain current (ID) of 300 mS/mm and ,1 A/mm, respectively. For the sample with 4.6 nm barrier thickness, a reduced gate leakage current (IGL) and a absolute value of the threshold voltage (Vth) of -1.2 V is detected. Radio frequency (RF) measurements of passivated samples lead to maximum current gain cut-off frequencies ft of 11 GHz and maximum oscillating frequencies fmax of 25 GHz. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High drain current and low on resistance normally-off-mode AlGaN/GaN junction HFETs with a p-type GaN gate contactPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008T. Fujii Abstract The normally-off-mode junction HFETs with a p-type GaN gate contact showing high drain current and an extremely large on/off ratio were successfully fabricated by MOVPE. The drain currents were found to be very sensitive to the surface of the u-AlGaN barrier exposed by RIE etching. A reproducible and stable high drain current was achieved using a very thin SiN passivation layer. The maximum drain current was 1.58×10,1 A/mm at VGS = 4 V, while the drain current at VGS = 0 V was as low as 1.45×10,8 A/mm. Therefore, an on/off ratio of 107 has been achieved. The sub-threshold swing was as small as 90 mV/dec.. The on resistance was 3.4 m,cm2, the threshold voltage was +0.45 V, and the breakdown voltage was over 325 V. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fabrication of enhancement-mode AlxGa1,xN/GaN junction heterostructure field-effect transistors with p-type GaN gate contactPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007T. Fujii Abstract We have investigated the device performance, such as the breakdown voltages between gate-source contacts and drain-source contacts, threshold voltage (Vth) and on resistance (RON), of enhancement-mode AlxGa1,xN/GaN junction heterostructure field-effect transistors (JHFET) with a p-type GaN gate. Fabricating an Al0.15Ga0.85N/GaN JHFET with a gate length of 2 ,m without surface passivation, we have achieved a completely enhancement-mode JHFET with a threshold voltage of +0.55 V, and breakdown voltages between gate-source and drain-source were over 100 V and 250 V, respectively. RON is as low as 4.5 m, · cm2 at VG = 3.0 V. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] AlGaN/GaN HEMT-based fully monolithic X-band low noise amplifierPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005R. Schwindt Abstract A fully monolithic AlGaN/GaN HEMT-based low noise amplifier is reported. The circuit demonstrated a noise figure of 3.5 dB, gain of 7.5 dB, input return loss of ,7.5 dB, and output return loss of ,15 dB at 8.5 GHz. The dc characteristics of individual 0.25-,m × 150-,m transistors were: maximum current density of 1.0 A/mm, maximum transconductance of 170 mS/mm and a threshold voltage of ,6.8 V. The devices have a typical short circuit current gain cutoff frequency of 24.5 GHz and a maximum oscillating frequency of 48 GHz. The devices demonstrated a minimum noise figure of 1.6 dB with an associated gain of 10.6 dB at 10 GHz. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||||||||||||||