ELECTRIC FIELD MICROSENSOR BASED ON THE STRUCTURE OF PIEZOELECTRIC INTERDIGITATED CANTILEVER BEAMS

This paper presents the design, fabrication, and preliminary experimental result of an electric field microsensor based on the structure of piezoelectric interdigitated cantilevers with staggered vertical vibration mode. The working principle of this electric field microsensor is demonstrated, and the induced charges and structural parameters of this microsensor are simulated by the finite element method. The electric field microsensor was fabricated by Micro-Electro Mechanical Systems(MEMS) technique. Each cantilever is a multilayer compound structure(Al/Si3N4/ Pt/PZT/Pt/ Ti/SiO 2/Si), and Piezoelectric, PieZ oelectric ceramic Transducer(PZT)(PbZ rxTi(1–x)O3) layer, prepared by sol-gel method, is used as the piezoelectric material to drive the cantilevers vibrating. This electric field microsensor was tested under the DC electric field with the field intensity from 0 to 5×104 V/m. The output voltage signal of the electric field microsensor has a good linear relationship to the intensity of applied electric field. The performance could be improved with the optimized design of structure, and reformative fabrication processes of PZT material.     

A new high voltage SOI LDMOS with triple RESURF structure

A novel triple RESURF（T-resurf） SOI LDMOS structure is proposed.This structure has a P-type buried layer.Firstly,the depletion layer can extend on both sides of the P-buried layer,serving as a triple RESURF and leading to a high drift doping and a low on-resistance.Secondly,at a high doping concentration of the drift region, the P-layer can reduce high bulk electric field in the drift region and enhance the vertical electric field at the drain side,which results in uniform bulk electric field distributions and an enhanced BV.The proposed structure is used in SOI devices for the first time.The T-resurf SOI LDMOS with BV = 315 V is obtained by simulation on a 6μm-thick SOI layer over a 2μm-thick buried oxide layer,and its R_sp is reduced from 16.5 to 13.8 mΩ·cm² in comparison with the double RESURF（D-resurf） SOI LDMOS.When the thickness of the SOI layer increases, T-resurf SOI LDMOS displays a more obvious effect on the enhancement of BV²/R_on.It reduces R_sp by 25%in 400 V SOI LDMOS and by 38%in 550 V SOI LDMOS compared with the D-resurf structure.     

具有补偿埋层的槽型埋氧层SOI高压器件新结构

A new silicon-on-insulator(SOI) high-voltage MOSFET structure with a compensation layer on the trenched buried oxide layer(CL T-LDMOS) is proposed.The high density inverse interface charges at the top surface of the buried oxide layer(BOX) enhance the electric field in the BOX and a uniform surface electric field profile is obtained,which results in the enhancement of the breakdown voltage(BV).The compensation layer can provide additional P-type charges,and the optimal drift region concentration is increased in order to satisfy the reduced surface electric field(RESURF) condition.The numerical simulation results indicate that the vertical electric field in the BOX increases to 6 MV/cm and the B V of the proposed device increases by 300%in comparison to a conventional SOI LDMOS,while maintaining low on-resistance.     

Exploration of photosensitive polyimide as the modification layer in thin film microcircuit

Positive type photosensitive polyimide is used as the modification layer in the thin film transistors production process.The photosensitive polyimide is not only used as the second insulating layer,it can also be used instead of a mask because of the photosensitivity.A suitable curing condition can help photosensitive polyimide form the high performance polyimide with orderly texture inside,and the performance of imidization depends on the precise control of temperature,time,and heat control during the curing process.Therefore,experiments of different stepped up heating tests are made,and the ability of protecting silicon dioxide is analyzed.     

Formaldehyde gas sensor based on TiO2 thin membrane integrated with nano silicon structure

An innovative formaldehyde gas sensor based on thin membrane type metal oxide of Ti O2 layer was designed and fabricated. This sensor under ultraviolet（UV） light emitting diode（LED） illumination exhibits a higher response to formaldehyde than that without UV illumination at low temperature. The sensitivities of the sensor under steady working condition were calculated for different gas concentrations. The sensitivity to formaldehyde of 7.14 mg/m³ is about 15.91 under UV illumination with response time of 580 s and recovery time of 500 s. The device was fabricated through micro-electro-mechanical system（MEMS） processing technology. First, plasma immersion ion implantation（PIII） was adopted to form black polysilicon, then a nanoscale TiO₂ membrane with thickness of 53 nm was deposited by DC reactive magnetron sputtering to obtain the sensing layer. By such fabrication approaches, the nanoscale polysilicon presents continuous rough surface with thickness of 50 nm, which could improve the porosity of the sensing membrane. The fabrication process can be mass-produced for the MEMS process compatibility.     

多层浮栅FET pH传感单元阈值电压敏感模型分析和讨论

Research into new pH sensors fabricated by the standard CMOS process is currently a hot topic. The new pH sensing multi-floating gate field effect transistor is found to have a very large threshold voltage, which is different from the normal ion-sensitive field effect transistor. After analyzing all the interface layers of the structure, a new sensitive model based on the Gauss theorem and the charge neutrality principle is created in this paper. According to the model, the charge trapped on the multi-floating gate during the process and the thickness of the sensitive layer are the main causes of the large threshold voltage. From this model, it is also found that removing the charge on the multi-floating gate is an effective way to decrease the threshold voltage. The test results for three different standard pH buffer solutions show the correctness of the model and point the way to solve the large threshold problem.     

基于过渡金属氧化物薄膜为连接层的叠层有机电制发光器件的数值模型

By utilizing a two-step process to express the charge generation and separation mechanism of the transition metal oxides （TMOs） interconnector layer, a numerical model was proposed for tandem organic light emitting diodes （OLEDs） with a TMOs thin film as the interconnector layer. This model is valid not only for an n-type TMOs interconnector layer, but also for a p-type TMOs interconnector layer. Based on this model, the influences of different carrier injection barriers at the interface of the electrode/organic layer on the charge generation ability of interconnector layers were studied. In addition, the distribution characteristics of carrier concentration, electric field intensity and potential in the device under different carrier injection barriers were studied. The results show that when keeping one carrier injection barrier as a constant while increasing another carrier injection barrier, carri- ers injected into the device were gradually decreased, the carrier generation ability of the interconnector layer was gradually reduced, the electric field intensity at the interface of the organic/electrode was gradually enhanced, and the electric field distribution became nearly linear： the voltage drops in two light units gradually became the same. Meanwhile, the carrier injection ability decreased as another carrier injection barrier increased. The simulation re- sults agree with the experimental data. The obtained results can provide us with a deep understanding of the work mechanism of TMOs-based tandem OLEDs.     

Organic thin film transistors with a SiO2/SiNx/SiO2 composite insulator layer

We have investigated a SiO₂/SiN_x/SiO₂ composite insulation layer structured gate dielectric for an organic thin film transistor（OTFT） with the purpose of improving the performance of the SiO₂ gate insulator. The SiO₂/SiN_x/SiO₂ composite insulation layer was prepared by magnetron sputtering.Compared with the same thickness of a SiO₂ insulation layer device,the SiO₂/SiN_x/SiO₂ composite insulation layer is an effective method of fabricating OTFT with improved electric characteristics and decreased leakage current.Electrical parameters such as carrier mobility by field effect measurement have been calculated.The performances of different insulating layer devices have been studied,and the results demonstrate that when the insulation layer thickness increases,the off-state current decreases.     

Recent progress of morphable 3D mesostructures in advanced materials

Soft robots complement the existing efforts of miniaturizing conventional,rigid robots,and have the potential to revolutionize areas such as military equipment and biomedical devices.This type of system can accomplish tasks in complex and time-varying environments through geometric reconfiguration induced by diverse external stimuli,such as heat,solvent,light,electric field,magnetic field,and mechanical field.Approaches to achieve reconfigurable mesostructures are essential to the design and fabrication of soft robots.Existing studies mainly focus on four key aspects:reconfiguration mechanisms,fabrication schemes,deformation control principles,and practical applications.This review presents a detailed survey of methodologies for morphable mesostructures triggered by a wide range of stimuli,with a number of impressive examples,demonstrating high degrees of deformation complexities and varied multi-functionalities.The latest progress based on the development of new materials and unique design concepts is highlighted.An outlook on the remaining challenges and open opportunities is provided.     

PI/Cr钝化对提高AlGaN/GaN HEMTs 击穿电压的研究

A novel AlGaN/GaN high electric mobility transistor（HEMT） with polyimide（PI）/chromium（Cr） as thepassivationlayerisproposedforenhancingbreakdownvoltageanditsDCperformanceisalsoinvestigated.The Cr nanoparticles firstly introduced in PI thin films by the co-evaporation can be used to increase the permittivity of PI film. The high-permittivity PI/Cr passivation acting as field plate can suppress the fringing electric field peak at the drain-side edge of the gate electrode. This mechanism is demonstrated in accord with measured results. The experimental results show that in comparison with the AlGaN/GaN HEMTs without passivation, the breakdown voltage of HEMTs with the PI/Cr composite thin films can be significantly improved, from 122 to 248 V.     

New application of polyimide in uncooled a-Si TFT infrared sensors

New application of polyimide (PI) is introduced in this paper. PI film of 27 μm is achieved, and the excellent thermal-isolation performance of the film is simulated by ANSYS. The surface of film is flat, which is suitable for the fabrication of other materials such as aluminum and silicon nitride. The PI film is used as thermal-isolation layer of uncooled a-Si thin film transistor infrared sensors in this research, and the fabrication process is greatly simplified.     

Plastic deformation magnetic assembly of out-of-plane structures using vapour phase hydrofluoric (HF) acid release

We report on the fabrication of out-of-plane microstructures using plastic deformation magnetic assembly (PDMA) and vapour phase HF release process. A 0.5 μm thin silicon oxide (SiO₂) layer deposited on blank silicon has been implemented as a sacrificial layer. A nickel film, 0.5 μm thick, deposited on top of the SiO₂ layer acts as the seed layer for the electrodeposition of a 4 μm nickel-iron permalloy film. The surface morphology and chemical composition of the permalloy film has been characterised using scanning electron microscopy and X-ray photoelectron spectroscopy (XPS), respectively. A dry vapour phase hydrofluoric (HF) acid release step has been employed to etch the sacrificial SiO₂, producing out-of-plane microstructures with high yield in the absence of a post-release drying step.     

Quad-cantilever microsensors with a low-cost single-sided micro-machining technique for trace chemical vapor detection

This paper presents a quad-cantilever microsensor for on-the-spot detection of ultra-low concentration chemical vapors. Compared with conventional dual-cantilever sensors, the quad-cantilever configuration can form a fully cantilever-formed Wheatstone-bridge that possesses a higher sensitivity of twofold and more balanced condition to compensate for environmental noise like temperature fluctuation or air flow. Besides, the four integrated micro-cantilevers are made of SiO₂, with each having a single crystal silicon piezoresistor fully encapsulated by SiO₂. Thus, the quad-lever sensor achieves a very low signal noise of 0.2 μV. For specific detection, sensitive molecule layer is self-assembled on two sensing cantilevers, with another two as reference. The sensors are micro-fabricated with a single-side process from the wafer front-side. With wet anisotropic etch used to release the piezoresistive cantilevers, the new fabrication technique features low-cost and high-yield. Self-assembled with a novel dual-branch specific mono-layer, about 100 ppt level trinitrotoluene (TNT) vapor has been rapidly and repeatedly detected.     

High‐Performance,Transparent Thin Film Hydrogen Gas Sensor Using 2D Electron Gas at Interface of Oxide Thin Film Heterostructure Grown by Atomic Layer Deposition

A high‐performance, transparent, and extremely thin (<15 nm) hydrogen (H₂) gas sensor is developed using 2D electron gas (2DEG) at the interface of an Al₂O₃/TiO₂ thin film heterostructure grown by atomic layer deposition (ALD), without using an epitaxial layer or a single crystalline substrate. Palladium nanoparticles (≈2 nm in thickness) are used on the surface of the Al₂O₃/TiO₂ thin film heterostructure to detect H₂. This extremely thin gas sensor can be fabricated on general substrates such as a quartz, enabling its practical application. Interestingly, the electron density of the Al₂O₃/TiO₂ thin film heterostructure can be tailored using ALD process temperature in contrast to 2DEG at the epitaxial interfaces of the oxide heterostructures such as LaAlO₃/SrTiO₃. This tunability provides the optimal electron density for H₂ detection. The Pd/Al₂O₃/TiO₂ sensor detects H₂ gas quickly with a short response time of <30 s at 300 K which outperforms conventional H₂ gas sensors, indicating that heating modules are not required for the rapid detection of H₂. A wide bandgap (>3.2 eV) with the extremely thin film thickness allows for a transparent sensor (transmittance of 83% in the visible spectrum) and this fabrication scheme enables the development of flexible gas sensors.     

Optically Sintered 2D RuO2 Nanosheets: Temperature‐Controlled NO2 Reaction

2D Ru oxide nanosheets (NSs) with optically punched nanoholes are synthesized and integrated on a flexible heating substrate, i.e., silver nanowire (Ag NW)‐embedded colorless polyimide (cPI) film, for application in wearable chemical sensors. Multiple discrete pores on the sub‐5‐nm scale are formed on the basal planes of Ru oxide NSs by irradiation of intense pulsed light. The chemical sensing characteristic of the porous Ru oxide NSs toward nitrogen dioxide (NO₂) is investigated under controlled temperatures by applying DC voltage to the Ag NW‐embedded cPI film. The improved NO₂ responding and recovery kinetics are achieved using the porous Ru oxide NSs with sensitivity of 1.124% at 20 ppm at a film temperature of 80.3 °C. A wireless patch‐type sensor module is developed to demonstrate wearable sensing of NO₂ using the Ru oxide NSs on Ag NW‐embedded cPI heating film. This work paved the new way for application of atomically thin and porous Ru oxide NSs in chemical sensors, which can detect hazardous species in real time.     

SnO2 gas sensor fabricated by low frequency alternating field electrophoretic deposition

SnO₂ thick film gas sensor has been prepared by applying low frequency (0.1 Hz) AC electric fields to a stable suspension of SnO₂ nanoparticles in acetylacetone. Parallel gold electrodes were used as the deposition substrate. Effect of CO, O₂ and H₂ gas exposure as well as ethanol vapor on conductivity of the SnO₂ film at 300 °C is investigated. Results show that the sensor is sensitive and its response is repeatable. This work shows that ACEPD can be used as an easy and cheap technique for fabrication of electronic devices such as ceramic-based gas sensors.     

A cost-effective flexible MEMS technique for temperature sensing

A simplified, cost-effective flexible micro-electronic-mechanical systems (MEMS) technology has been developed for realizing a temperature-sensing array on a flexible polyimide substrate. The fabrication technique utilized liquid polyimide to form flexible film on the rigid silicon wafer using a temporary carrier during the fabrication. The platinum thin film is employed as temperature sensitive material and 8×8 temperature-sensing arrays were micromachined on the polyimide, from which the silicon wafer carrier was removed at the end of fabrication. The platinum thin film temperature sensor exhibits excellent linearity and its temperature coefficient of resistance reaches 0.00291 °C⁻¹. Because of the effective thermal isolation, the flexible temperature sensors show a high sensitivity of 1.12 Ω/°C at 10 mA to the constant drive current. The flexible MEMS technology based on liquid polyimide enables the development of flexible, compliant, robust, and multi-modal sensor skins for many other important applications, such as robotics, biomedicine, and wearable microsystems.     

Excimer Laser Projection Photoablation Patterning of Metal Thin Films for Fabrication of Microelectronic Devices and Displays

A nonlithographic process is demonstrated for patterning Al, Cr, Cu, Ni, Ti, and W thin films, which are widely used in microelectronic and display fabrication. A projection photoablation process using 248-nm-deep ultraviolet radiation from a KrF excimer laser was used to pattern a polyimide film coated on a SiN layer deposited on glass. The photoablation-patterned polyimide film was used as a sacrificial layer in a lift-off patterning process for the metal films, which resulted in clean metal patterns with fine line-edge definition being fabricated after lift-off. This process provides a simpler and more economical patterning technique compared to conventional lithography methods, eliminating the developing and etching steps.     

Cu(In,Ga)Se2 solar cell grown on flexible polymer substrate with efficiency exceeding 17%

Development of a Cu(In,Ga)Se₂ thin film solar cell on a polyimide film with a conversion efficiency of 17.1%, measured under standard test conditions at the European Solar Test Installation (ESTI) of the Joint Research Centre (JRC) of the European Commission, Ispra, is reported. The drastic improvement from the previous record of 14.1% efficiency is attributed to a more optimized compositional grading, better structural and electronic properties of the absorber layer as well as reduced reflection losses. Basic film and device properties, which led to the improvement in the efficiency record of flexible solar cells are presented for the new process and compared to the old process. Copyright © 2011 John Wiley & Sons, Ltd.     

Curing of polyimide and the effect of the TEOS SiO2 barrier layer on the electromigration of sputtered Cu with polyimide passivation

The curing process of polyimide and the electromigration of copper films with polyimide (PI) passivation are studied. Thermal analysis of polyimide suggests that imidization completes at ∼200°C with an endothermic reaction associated with the breaking of the C-OH and N-H bonds as revealed by Fourier transformation infrared spectroscopy (FTIR). Although there is 89.8% weight loss when PI is heated from 20°C to 200°C, outgassing of PI passivation is still observed at higher temperatures. Carbon, nitrogen, and oxygen atoms diffuse into Cu during thermal processing of PI/Cu films. The tetraethyl orthosilicate (TEOS) SiO₂ films are used as the barrier layer between PI and Cu to retard the poisoning of Cu. The effect of TEOS SiO₂ film on electromigration of Cu is investigated.