Organic field-effect transistor with extended indium tin oxide gate structure for selective pH sensing

In this study, organic field-effect transistors (OFETs) with extended gate structure were fabricated for selective pH sensing applications. Indium tin oxide (ITO) was used as extended gate electrode as well as an active layer for H⁺ sensing. The threshold voltage of the fabricated ion-selective OFET was varied by the changes in the electrochemical potential at the ITO electrode surface upon its exposure to buffer solutions with variable pH values. The sensor showed excellent linearity and a high sensitivity of 57–59 mV/pH in the pH range of 2–12. The selectivity of the ITO sensing layer to H⁺ ions was also investigated by measuring the interfering effect of Ca²⁺ and K⁺ ions in the buffer pH solutions. The results showed that the Ca²⁺ and K⁺ ions weakly interfere with the selective pH sensing of the ITO-extended gate OFET sensor device.     

Bipolar Tetraarylsilanes as Universal Hosts for Blue,Green, Orange,and White Electrophosphorescence with High Efficiency and Low Efficiency Roll‐Off

A series of tetraarylsilane compounds, namely p‐BISiTPA ( 1 ), m‐BISiTPA ( 2 ), p‐OXDSiTPA ( 3 ), m‐OXDSiTPA ( 4 ), are designed and synthesized by incorporating electron‐donating arylamine and electron‐accepting benzimidazole or oxadiazole into one molecule via a silicon‐bridge linkage mode. Their thermal, photophysical and electrochemical properties can be finely tuned through the different groups and linking topologies. The para‐disposition compounds 1 and 3 display higher glass transition temperatures, slightly lower HOMO levels and triplet energies than their meta‐disposition isomers 2 and 4 , respectively. The silicon‐interrupted conjugation of the electron‐donating and electron‐accepting segments gives these materials the following advantages: i) relative high triplet energies in the range of 2.69–2.73 eV; ii) HOMO/LUMO levels of the compounds mainly depend on the electron‐donating and electron‐accepting groups, respectively; iii) bipolar transporting feature as indicated by hole‐only and electron‐only devices. These advantages make these materials ideal universal hosts for multicolor phosphorescent OLEDs. 1 and 3 have been demonstrated as universal hosts for blue, green, orange and white electrophosphorescence, exhibiting high efficiencies and low efficiency roll‐off. For example, the devices hosted by 1 achieve maximum external quantum efficiencies of 16.1% for blue, 22.7% for green, 20.5% for orange, and 19.1% for white electrophosphorescence. Furthermore, the external quantum efficiencies are still as high as 14.2% for blue, 22.4% for green, 18.9% for orange, and 17.4% for white electrophosphorescence at a high luminance of 1000 cd m^?2. The two‐color, all‐phosphor white device hosted by 3 acquires a maximum current efficiency of 51.4 cd A^?1, and a maximum power efficiency of 51.9 lm W^?1. These values are among the highest for single emitting layer white PhOLEDs reported till now.     

Poly(diketopyrrolopyrrole‐benzothiadiazole) with Ambipolarity Approaching 100% Equivalency

As a characteristic feature of conventional conjugated polymers, it has been generally agreed that conjugated polymers exhibit either high hole transport property (p‐type) or high electron transport property (n‐type). Although ambipolar properties have been demonstrated from specially designed conjugated polymers, only a few examples have exhibited ambipolar transport properties under limited conditions. Furthermore, there is, as yet, no example with ‘equivalent’ hole and electron transport properties. We describe the realization of an equivalent ambipolar organic field‐effect transistor (FET) by using a single‐component visible–near infrared absorbing diketopyrrolopyrrole (DPP)‐benzothiadiazole (BTZ) copolymer, namely poly[3,6‐dithiene‐2‐yl‐2,5‐di(2‐decyltetradecyl)‐pyrrolo[3,4‐c]pyrrole‐1,4‐dione‐5’,5’’‐diyl‐alt‐benzo‐2,1, 3‐thiadiazol‐4,7‐diyl] ( PDTDPP‐alt‐BTZ ). PDTDPP‐alt‐BTZ shows not only ideally balanced charge carrier mobilities for both electrons (?_e = 0.09 cm²V^?1s^?1) and holes (?_h = 0.1 cm²V^?1s^?1) but also its inverter constructed with the combination of two identical ambipolar FETs exhibits a gain of ～35 that is much higher than usually obtained values for unipolar logic.     

微波、毫米波GaN HEMT与MMIC的新进展

综述了近几年微波、毫米波氮化镓高电子迁移率晶体管(GaN HEMT)与单片微波集成电路(MMIC)在高效率、宽频带、高功率和先进热管理等方面的应用创新进展.介绍了基于GaN HEMT器件所具有的高功率密度和高击穿电压,采用波形工程原理设计的各类开关模式的高效率功率放大器,以及基于GaN HEMT器件的高功率密度、高阻抗的特点与先进的宽带拓扑电路和功率合成技术相结合的宽频带和高功率放大器.详细介绍了微波高端和毫米波段的高效率、宽频带和高功率放大器,多功能电路和多功能集成的GaN MMIC.最后阐述了由于GaN HEMT的功率密度是其他半导体器件的数倍,其先进热管理的创新研究也成为热点.     

n型纳米非对称DG-TFET阈值电压特性研究

n型纳米非对称双栅隧穿场效应晶体管(DG-TFET)速度快、功耗低,在高速低功耗领域具有很好的应用前景,但其阈值电压的表征及其模型与常规MOSFET不同.在深入研究n型纳米非对称DG-TFET的阈值特性基础上,通过求解器件不同区域电场、电势的方法,建立了n型纳米非对称DG-TFET器件阈值电压数值模型,探讨了器件材料物理参数以及漏源电压对阈值电压的影响,通过与Silvaco Atlas的仿真结果比较,验证了模型的正确性.研究表明,n型纳米非对称DG-TFET的阈值电压分别随着栅介质层介电常数的增加、硅层厚度的减薄以及源漏电压的减小而减小,而栅长对其阈值电压的影响有限.该研究对纳米非对称DG-TFET的设计、仿真及制造有一定的参考价值.     

晶体管式精密电阻点焊电源的设计

为满足微型零件焊接对焊接能量精密性、快速性和稳定性的要求,设计了一种高频晶体管式电阻点焊电源。电源包含半桥逆变恒流充电部分和高频斩波输出部分,逆变频率为100 k Hz,通过脉冲宽度调制(Pulse Width Modulation,PWM)和增量式比例积分微分(Proportion Integration Differentiation,PID)控制技术,实现了电容组恒流快速充电;斩波频率为100 k Hz,大大提高了焊接输出能量调节响应速度和控制精度。试验结果表明,电容组最大充电电流为100 A,充电电压为30 V,充电时间小于100 ms;电源具有恒电流、恒电压和恒功率输出模式,焊接电流上升速度达到50 A/μs,放电脉冲可在1 ms内实现稳定输出,实际焊接效果良好,在精密焊接中具有明显优势。     

Sputtered oxides used for passivation layers of amorphous InGaZnO thin film transistors

Four sputtered oxide films (SiO₂, Al₂O₃, Y₂O₃ and TiO₂) along with their passivating amorphous InGaZnO thin film transistors (a-IGZO TFTs) were comparatively studied in this paper. The device passivated by an Al₂O₃ thin film showed both satisfactory performance (μ_FE=5.3 cm²/V s, I_on/I_off>10⁷) and stability, as was probably related to smooth surface of Al₂O₃ thin films. Although the performance of the a-IGZO TFTs with a TiO₂ passivation layer was also good enough (μ_FE=3.5 cm²/V s, I_on/I_off>10⁷), apparent V_th shift occurred in positive bias-stress tests due to the abnormal interface state between IGZO and TiO₂ thin films. Sputtered Y₂O₃ was proved no potential for passivation layers of a-IGZO TFTs in this study. Despite unsatisfactory performance of the corresponding a-IGZO TFT devices, sputtered SiO₂ passivation layer might still be preferred for its high deposition rate and excellent transparency which benefit the mass production of flat panel displays, especially active-matrix liquid crystal displays.     

Stabilization of space charge polarization in ion-dispersed gate dielectric layer of organic transistors by ultraviolet illumination for write-once read-many memory

In this work, a new type organic field effect transistor (OFET) based write-once read-many memory (WORM) device was developed. The device uses an ultraviolet (UV) cross-linkable matrix polymer mixed with ionic compounds to form an ion-dispersed gate dielectric layer. Under an applied gate voltage bias, migration of cations and anions in opposite directions forms space charge polarization in the gate dielectric layer, resulting in change of the electrical characteristics. It is shown that, with UV illumination to cross-link the matrix polymer, the formed space charge polarization can be stabilized. Therefore, the OFET can be operated as a WORM with the applied voltage bias to define the polarization and in turn the stored data, and the UV illumination to stabilize the stored data.     

Solution processable bilayered gate dielectric towards flexible organic thin film transistors

In this study, we have successfully explored the potential of a new bilayer gate dielectric material, composed of Polystyrene (PS), Pluronic P123 Block Copolymer Surfactant (P123) composite thin film and Polyacrylonitrile (PAN) through fabrication of metal insulator metal (MIM) capacitor devices and organic thin film transistors (OTFTs). The conditions for fabrication of PAN and PS-P123 as a bilayer dielectric material are optimized before employing it further as a gate dielectric in OTFTs. Simple solution processable techniques are applied to deposit PAN and PS-P123 as a bilayer dielectric layer on Polyimide (PI) substrates. Contact angle study is further performed to explore the surface property of this bilayer polymer gate dielectric material. This new bilayer dielectric having a k value of 3.7 intermediate to that of PS-P123 composite thin film dielectric (k ∼ 2.8) and PAN dielectric (k ∼ 5.5) has successfully acted as a buffer layer by preventing the direct contact between the organic semiconducting layer and high k PAN dielectric. The OTFT devices based on α,ω-dihexylquaterthiophene (DH4T) incorporated with this bilayer dielectric, has demonstrated a hole mobility of 1.37 × 10⁻² and on/off current ratio of 10³ which is one of the good values as reported before. Several bending conditions are applied, to explore the charge carrier hopping mechanism involved in deterioration of electrical properties of these OTFTs. Additionally, the electrical performance of OTFTs, which are exposed to open atmosphere for five days, can be interestingly recovered by means of re-baking them respectively at 90 °C.     

1 Volt organic transistors with mixed self-assembled monolayer/Al2O3 gate dielectrics

Control of the threshold voltage and the subthreshold swing is critical for low voltage transistor operation. In this contribution, organic field-effect transistors (OFETs) operating at 1 V using ultra-thin (∼4 nm), self-assembled monolayer (SAM) modified aluminium oxide layers as the gate dielectric are demonstrated. A solution-processed donor–acceptor semiconducting polymer poly(3,6-di(2-thien-5-yl)-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione)thieno[3,2-b]thiophene) (PDPP2TTT) is used as the active layer. It is shown that the threshold voltage of the fabricated transistors can be simply tuned by carefully controlling the composition of the applied SAM. The optimised OFETs display threshold voltages around 0 V, low subthreshold slopes (150 ± 5 mV/dec), operate with negligible hysteresis and show average saturated field-effect mobilities in excess of 0.1 cm²/V s at 1 V.