Interface engineering for improving optical switching in a diarylethene-channel transistor

Photochromic diarylethene (DAE) molecules were employed as the channel layer of a field-effect transistor, where the drain current was effectively modulated by the reversible phase transition between a semiconductor (closed-ring) and an insulator (open-ring) under ultraviolet or visible light irradiation. Our goal was the further improvement of optical switching properties by interface engineering. First, we reduced the hole injection barrier by introducing an α-sexithiophene (6T) thin film at the interface between the source–drain electrodes and the DAE channel layer. As a result, the threshold voltage of the DAE-FETs was greatly reduced from −64 to −4 V. Second, we improved the optical switching performance by the surface treatment of a SiO₂ gate insulator with poly(methyl methacrylate) (PMMA). The drain current was unchanged even after 10 cycles of optical switching in contrast to the rapid degradation found with untreated DAE transistors. The combination of these improvements and interdigitated source–drain electrodes eventually resulted in a light irradiation driven on/off ratio of over 10³. Significantly, the light-induced on/off ratio was comparable to that driven by an electrical field, which satisfies the requirement for industrial optical applications. Our findings will provide useful ways of realizing high-performance optical switching transistors.     

MoS2 Tribotronic Transistor for Smart Tactile Switch

A novel tribotronic transistor has been developed by vertically coupling a single‐electrode mode triboelectric nanogenerator and a MoS₂ field effect transistor. Once an external material contacts with or separates from the device, negative charges are induced by triboelectrification on the surface of the polymer frictional layer, which act as a “gate” voltage to modulate the carrier transport in the MoS₂ channel instead of the conventional applied gate voltage; the drain‐source current can be tuned in the range of 1.56–15.74 μA, for nearly ten times. The application of this MoS₂ tribotronic transistor for the active smart tactile switch is also demonstrated, in which the on/off ratio can reach as high as ≈16 when a finger touches the device and the increased drain‐source current is sufficient to light two light‐emitting diodes. This work may provide a technique route to utilize the 2D materials based tribotronic transistors in MEMS, nanorobotics, and human–machine interfacing.     

Evidence of optical generation of minority carriers from saturated MOS transistors

Minority carrier injection into the substrate by a MOS transistor operating in saturation presents a reliability problem in dynamic memory circuits such as RAM's and CCD's. The effect has been studied by measuring the substrate and drain currents of stressed transistors as a function of gate and drain voltages, firstly by the accumulation of minority carriers in a charge coupled device, and secondly by the direct detection of light from the drain region of a transistor. These results suggest that light emission associated with multiplication in the drain region is more important than the secondary impact ionization mechanism in the generation of minority carriers.     

Low‐Voltage Operational,Low‐Power Consuming,and High Sensitive Tactile Switch Based on 2D Layered InSe Tribotronics

Electronics based on layered indium selenide (InSe) channels exhibit promising carrier mobility and switching characteristics. Here, an InSe tribotronic transistor (denoted as w/In InSe T‐FET) obtained through the vertical combination of an In‐doped InSe transistor and triboelectric nanogenerator is demonstrated. The w/In InSe T‐FET can be operated by adjusting the distance between two triboelectrification layers, which generates a negative electrostatic potential that serves as a gate voltage to tune the charge carrier transport behavior of the InSe channel. Benefiting from the surface charging doping of the In layer, the w/In InSe T‐FET exhibits high reliability and sensitivity with a large on/off current modulation of 10⁶ under a low drain–source voltage of 0.1 V and external frictional force. To demonstrate its function as a power‐saving tactile sensor, the w/In InSe T‐FET is used to sense “INSE” in Morse code and power on a light‐emitting diode. This work reveals the promise of 2D material–based tribotronics for use in nanosensors with low power consumption as well as in intelligent systems.     

Improved thermal stability in photochromism-based optically controllable organic thin film transistor

Thermally induced structural change in photoisomerization molecules is a serious obstacle to the development of optically controllable organic field-effect transistors (OFETs). This is because the thermal relaxation of molecular structures degrades photo-induced change in drain current and removes the memory function. To deal with this issue, a naphthopyran (NP) derivative, namely 3,13-dihydro-3-(4-triphenylaminyl)-3,13-diphenylbenzopyrano[5,6-a]carbazole (NP-TPAC) was tested that displays pseudo p-type photochromism at room temperature. The NP-TPAC-doped poly(triarylamine) (PTAA) film exhibited a reversible change in transistor properties; the drain current was reduced by ultraviolet (UV) and returned to its original value by visible (VIS) light irradiation. Importantly, no change in the drain current was observed at room temperature for more than 30 h under dark conditions. This was because the open-ring trans–trans (TT) isomer of NP-TPAC is thermally stable owing to the CH-π interaction and the steric force exerted by the phenyl ring of the carbazole unit onto the double bond responsible for the thermal back reaction. In other words, the thermal stability of photochromism-based optical devices can be greatly improved by adopting an appropriate molecular design.     

一种能有效抑制背光照影响的非晶硅薄膜晶体管

提出了一种能有效抑制背光照影响的非晶硅薄膜晶体管结构。详细地分析了源、漏电极接触区和沟通区内载流子的输运特性。论述了在背光照射下,这种结构的ＴＦＴ能有铲抑制关态电流上升的机理。研究了有源层ａ－Ｓｉ：Ｈ膜层厚度对ＴＦＴ关态电流和开态电流的影响。检测辽种结构ＴＦＴ在暗态和背照射下的静态特性。     

WSe2场效应晶体管的源漏接触特性研究

二硒化钨(WSe2)具有双极导电特性,可以通过外界掺杂或改变源漏金属来调节载流子传输类型,是一类特殊的二维纳米材料,有望在未来集成电路中成为硅(Si)的替代材料.文章采用理论与实验相结合的方式系统分析了 WSe2场效应晶体管中的源漏接触特性对器件导电类型及载流子传输特性的影响,通过制备不同金属作为源漏接触电极的WSe2场效应晶体管,发现金属/WSe2接触的实际肖特基接触势垒高低极大地影响了晶体管的开态电流.源漏金属/WSe2接触特性不仅取决于接触前理想的费米能级差,还受到界面特性,特别是费米能级钉扎效应的影响.     

Photo-induced storage and mask-free arbitrary micro-patterning in solution-processable and simple-structured photochromic organic light-emitting diodes

A photochromic diarylethene-based compound BMTA, which undergoes a reversible conversion between ring- open and closed isomers by alternating UV and visible light illumination, has been designed and synthesized. By utilizing a mask-free Digital Micro-mirror Device (DMD) micro-lithography system, arbitrary micro-photopatterning in polymer films doped with BMTA can be easily obtained with UV light writing. This recorded photo information can easily be erased by further visible light irradiation. The reversible and rewritable optical storage is based on photo-switched intermolecular energy transfer between the emissive host and the ring-closed isomer c-BMTA. Furthermore, the solution-processable organic light-emitting devices (OLEDs) with the single emitting layer doped with BMTA were fabricated, which exhibit rewritable memory behavior with light control. The luminescence and current density decrease significantly upon UV light irradiation, and recover by further visible light illumination. This is because the hole trapping is much facilitated in closed-ring isomer based devices, due to elevated HOMO level of c-BMTA. Without incorporating any cross-linking layer, the maximum luminescence and current density on/off ratios of this solution-processable and simple-structured device are 1.9 × 10³ and 1.4 × 10², respectively. Arbitrary micro-photolithography of OLEDs by DMD system has also been demonstrated, which shows great prospects in large-scale production of high resolution OLED displays.     

Schottky junction transistor-micropower circuits at GHz frequencies

Numerical simulations of a new micropower transistor configuration are presented. The transistor is a majority carrier device that operates as a current-controlled current-source. Results from a 0.5 μm gate length device indicate a cutoff frequency in the GHz range, for drain currents appropriate to micropower circuit applications     

Full-band Monte Carlo investigation of hot carrier trends in thescaling of metal-oxide-semiconductor field-effect transistors

A full-band Monte Carlo (MC) device simulator has been used to study the effects of device scaling on hot electrons in different types of n-channel metal-oxide-semiconductor field-effect transistor (MOSFET) structures. Simulated devices include a conventional MOSFET with a single source/drain implant, a lightly-doped drain (LDD) MOSFET, a silicon-on-insulator (SOI) MOSFET, and a MOSFET built on an epitaxial layer on top of a heavily-doped ground plane. Different scaling techniques have been applied to the devices, to analyze the effects on the electric field and on the energy distributions of the electrons, as well as on drain, substrate, and gate currents. The results provide a physical basis for understanding the overall behavior of impact ionization and gate oxide injection and how they relate to scaling. The observed nonlocality of transport phenomena and the nontrivial relationship between electric fields and transport parameters indicate that simpler models cannot adequately predict hot carrier behavior at the channel lengths studied (sub-0.3-μm). In addition, our results suggest that below 0.15 μm, the established device configurations (e.g. LDD) that are successful at suppressing the hot carrier population for longer channel lengths, become less useful and their cost-effectiveness for future circuit applications needs to be reevaluated     

一种廉价电极的并五苯场效应晶体管

采用底栅顶接触结构,研究制备了以并五苯为有源层、聚甲基丙烯酸甲酯(PMMA)为绝缘层的全有机场效应晶体管(OFET),其中绝缘层采用溶液旋涂法制备,电极采用MoO3/Al双层电极。与传统采用单一Au为电极的器件相比,采用双层电极的器件性能大幅提高,经测试,器件的迁移率达到了0.133cm2/Vs,开关电流比可以达到2.61×105。对采用MoO3修饰层提高性能的作用机理进行了详细论证。     

Heat Generation and Transport in Nanometer-Scale Transistors

As transistor gate lengths are scaled towards the 10-nm range, thermal device design is becoming an important part of microprocessor engineering. Decreasing dimensions lead to nanometer-scale hot spots in the transistor drain region, which may increase the drain series and source injection electrical resistances. Such trends are accelerated by the introduction of novel materials and nontraditional transistor geometries, including ultrathin body, FinFET, or nanowire devices, which impede heat conduction. Thermal analysis is complicated by subcontinuum phenomena including ballistic electron transport, which reshapes the heat generation region compared with classical diffusion theory predictions. Ballistic phonon transport from the hot spot and between material boundaries impedes conduction cooling. The increased surface to volume ratio of novel transistor designs also leads to a larger contribution from material boundary thermal resistance. This paper surveys trends in transistor geometries and materials, from bulk silicon to carbon nanotubes, along with their implications for the thermal design of electronic systems.     

Organic light-emitting transistors with split-gate structure and PN-hetero-boundary carrier recombination sites

Novel light-emitting transistors (OLETs) with the split-gate electrode divided into two parts for independent control of electron and hole were devised, in addition to the PN-hetero-boundary combined with the electron and hole transport materials along carrier channels. With this device structure, the on/off ratio of 1000 or more in the current and the luminance were achieved. Which is 100 times or more large compared with earlier reported single-gate type PN-hetero-boundary light-emitting transistor [N. Suganuma, N. Shimoji, Y. Oku, K. Matsushige, Novel organic light-emitting transistors with PN-heteroboundary carrier recombination sites fabricated by lift-off patterning of organic semiconductor thin films, J. Mater. Res. 22 (2007) 2982; N. Suganuma, N. Shimoji, PCT Int. Appl. WO2007/010925; N. Suganuma, PCT Int. Appl. WO2007/026703]. In this device, the luminance of about 100 cd/m² was obtained at 15 V in the source–source voltage (also known as the source–drain voltage) with the turn-on voltage of less than 10 V. The horizontal PN-hetero-boundary structure was implemented for the first time by using the photolithographic patterning of the organic semiconductor thin-films. This patterning technique can be applied in fabricating not only organic light-emitting transistors reported in this article but also organic integrated circuit or organic display.     

Phosphorene field-effect transistors using high-k gate dielectrics of epitaxial SrTiO3 layers grown on Nb-doped SrTiO3 substrates

Epitaxial SrTiO₃ (STO) thin film as a gate dielectric layer was grown on single crystalline (100) Nb-doped SrTiO₃ substrate. On the 100-nm-thick STO gate dielectric layer, a 5-nm-thick phosphorene sheet channel layer was exfoliated from a bulk crystal. A phosphorene field-effect transistor (P-STO-FET) was prepared by the formation of 90-nm-thick Au source/drain (S/D) contacts. The P-STO-FET exhibited the transport characteristics of a p-type transistor with a mobility of approximately 376 cm⁻²/Vs and an on/off ratio of approximately 10³. Furthermore, it was experimentally confirmed that the mobility of the P-STO-FET was significantly influenced by the flatness of the phosphorene sheet.     

Inkjet‐Printed Single‐Droplet Organic Transistors Based on Semiconductor Nanowires Embedded in Insulating Polymers

Fabrication of organic field‐effect transistors (OFETs) using a high‐throughput printing process has garnered tremendous interest for realizing low‐cost and large‐area flexible electronic devices. Printing of organic semiconductors for active layer of transistor is one of the most critical steps for achieving this goal. The charge carrier transport behavior in this layer, dictated by the crystalline microstructure and molecular orientations of the organic semiconductor, determines the transistor performance. Here, it is demonstrated that an inkjet‐printed single‐droplet of a semiconducting/insulating polymer blend holds substantial promise as a means for implementing direct‐write fabrication of organic transistors. Control of the solubility of the semiconducting component in a blend solution can yield an inkjet‐printed single‐droplet blend film characterized by a semiconductor nanowire network embedded in an insulating polymer matrix. The inkjet‐printed blend films having this unique structure provide effective pathways for charge carrier transport through semiconductor nanowires, as well as significantly improve the on‐off current ratio and the environmental stability of the printed transistors.     

Two-dimensional analysis of substrate-related kink phenomena inGaAs MESFET's

Two-dimensional simulations of GaAs MESFET's are made in which impact ionization of carriers and impurity compensation by deep levels in semi-insulating substrates are considered. It is shown that in cases with high acceptor densities in the semi-insulating substrates, a steep increase in output conductance with the drain voltage (“kink”) arises because holes that are generated by impact ionization flow into the substrates and are captured by the deep levels to modulate the space-charge distributions. In cases with low acceptor densities in the substrates, a sudden increase in drain currents due to conductivity modulation in the substrates is observed. It is concluded that carrier trapping and current transport in the semi-insulating substrate should be taken into account when considering kink effects and/or breakdown phenomena in GaAs MESFET's     

A Piezotronic and Magnetic Dual-Gated Ferroelectric Semiconductor Transistor

Piezotronics is the coupling effect of the piezoelectric and semiconductor properties; however, the piezoelectric constant of the piezoelectric semiconductor is relatively small while the ferroelectric materials with large piezoelectric constant typically possess weak semiconductor properties, thus limiting the effective coupling coefficient of the piezotronic materials and devices. Here, a piezotronics and magnetic dual-gated ferroelectric semiconductor transistor (PM-FEST) is fabricated by Terfenol-D, aluminum oxide (Al₂O₃), and ferroelectric semiconductor α-In₂Se₃, which has a large piezoelectric coefficient, room-temperature ferroelectricity, and dipole locking. The charge carrier transport and corresponding drain current of the PM-FEST can be directly modulated by either the applied magnetic field or external strain. At a low magnetic field (<200 mT), the maximum current on/off ratio of α-In₂Se₃ based PM-FEST is as high as 1700%. Compared with traditional piezotronic devices, the PM-FEST demonstrates a higher gauge factor (2.3 × 10⁴) than that of the piezoelectric semiconductors. This work provides a possibility of realizing magnetism-modulated electronics in semiconductors by exploiting the coupling of piezotronics and magnetostriction.     

Optically Tunable Field Effect Transistors with Conjugated Polymer Entailing Azobenzene Groups in the Side Chains

Semiconducting conjugated polymers with photoswitching behavior are highly demanded for field‐effect transistors (FETs) with tunable electronic properties. Herein a new design strategy is established for photoresponsive conjugated polymers by incorporating photochromic units (azobenzene) into the flexible side alkyl chains. It is shown that azobenzene groups in the side chains of the DPP (diketopyrrolopyrrole)‐quaterthiophene polymer ( PDAZO ) can undergo trans/cis photoisomerization in fully reversible and fast manner. Optically tunable FETs with bistable states are successfully fabricated with thin films of PDAZO . The drain‐source currents are reduced by 80.1% after UV light irradiation for ≈28 s, which are easily restored after further visible light irradiation for ≈33 s. Such fast optically tunable FETs are not reported before. Moreover, such current photomodulation can be implemented for multiple light irradiation cycles with good photofatigue resistance. Additionally, thin film charge mobility of PDAZO can be reversibly modulated by alternating UV and visible light irradiations. On the basis of theoretical calculations and GIWAXS data, it is hypothesized that the dipole moment and configuration changes associated with the trans‐/cis‐photoisomerization of azobenzene groups in PDAZO can affect the respective intra‐chain and inter‐chain charge transporting, which is responsible for the optically tunable behavior for FETs with thin films of PDAZO .     

A novel PMOS SOI polysilicon transistor

An advanced silicon-on-insulator (SOI) PMOS polysilicon transistor, featuring an inverted gate electrode and self-aligned source/drain and gate/channel regions, is developed and characterized. Selective oxidation is used to form self-aligned thin polysilicon channel regions with thicker source/drain polysilicon regions. The gate electrode is formed by a high-energy boron implant into the underlying silicon substrate. Since the gate oxide is formed over single-crystal silicon rather than polysilicon, an improvement in gate oxide integrity is possible. The resulting SOI PMOS device is suitable for high-density static random access memory (SRAM) circuit applications and exhibits excellent short-channel behavior with an on/off current ratio exceeding six orders of magnitude     

A novel composite UV/blue photodetector based on CMOS technology: design and simulation

A novel composite ultraviolet （UV）/blue photodetector is proposed in this paper. Lateral ring-shaped PN junction is used to separate photogenerated carriers and inject the non-equilibrium excess carriers to the bulk, changing the bulk potential and shifting the threshold voltage of the metal-oxide-semiconductor field-effect transistor （MOSFET） as well as the drain current. Numerical simulation is carried out, and the simulation results show that the composite photodetector has the enhanced responsivity for UV/blue spectrum. It exhibits very high sensitivity to weak and espe- cially ultra-weak light. A responsivity of 7000 A/W is obtained when the photodetector is illuminated under incident optical power of 0.01 μW. As a result, this proposed combined photodetector has great potential for UV/blue and ul- tra-weak light applications.