Trap states induced by reactive ion etching in AlGaN/GaN high-electron-mobility transistors

Frequency-dependent conductance measurements were carried out to investigate the trap states induced by reactive ion etching in A1GaN/GaN high-electron-mobility transistors （HEMTs） quantitatively. For the non-recessed HEMT, the trap state density decreases from 2.48 × 1013 cm-2.eV-1 at an energy of 0.29 eV to 2.79 × 1012 cm-2.eV-1 at ET = 0.33 eV. In contrast, the trap state density of 2.38 × 1013-1.10× 1014 cm-2.eV-1 is located at ET in a range of 0.30-0.33 eV for the recessed HEMT. Thus, lots of trap states with shallow energy levels are induced by the gate recess etching. The induced shallow trap states can be changed into deep trap states by 350 ℃ annealing process. As a result, there are two different types of trap sates, fast and slow, in the annealed HEMT. The parameters of the annealed HEMT are ET = 0.29-0.31 eV and DT = 8.16× 1012-5.58 × 1013 cm-2.eV-1 for the fast trap states, and ET = 0.37-0.45 eV and DT = 1.84×1013- 8.50 × 1013 cm-2.eV-1 for the slow trap states. The gate leakage currents are changed by the etching and following annealing process, and this change can be explained by the analysis of the trap states.

Transfer of Machined Patterns on an Aluminum Plate to Pyrex Glass Using Reactive Ion Etching SF_(6) Plasma without Masks

A method for etching the surface of a Pyrex glass substrate using the Reactive Ion Etching process without the use of masks is reported. Variations in the machined surface on an auxiliary plate, manufactured in aluminum and placed below a Pyrex glass slide, were transferred to the upper surface of the substrate. SF6 as etching gas and low pressure chamber to promote the increase of mean free path of ions were used. Two etching ratios were found, general, that affects the entire surface of the substrate, and differential, which generates the relief on the surface of the glass. Differential etching depth showed a linear behavior with respect to time;the mean differential etching rate obtained was 43 nm/min. The same phase between the auxiliary plate machining and the etched pattern on the substrate is preserved. With this technique it was possible to manufacture convex and concave surfaces;some examples are given. The arithmetic mean roughness achieved with the proposed method was found to be N1 class, ideal for the development of optical corrector plates.

A sliding-mode triboelectric nanogenerator with chemical group grated structure by shadow mask reactive ion etching

With the support by the National Natural Science Foundation of China,a collaboration by the research groups led by Prof.Cheng Gang(程纲)from Henan University and Prof.Wang Zhonglin(王中林)from Beijing Institute of Nanoenergy and Nanosystems,Chinese Academy of Sciences,invents'a sliding-mode triboelectric nanogenerator with chemical group grated structure by shadow mask reactive ion etching',which was published in ACS Nano(2017,11(9):8796-8803).

A photoluminescence study of plasma reactive ion etching-induced damage in GaN

GaN films with reactive ion etching （RIE） induced damage were analyzed using photoluminescence （PL）. We observed band-edge as well as donor-acceptor peaks with associated phonon replicas, all in agreement with previous studies. While both the control and damaged samples have their band-edge peak location change with temperature following the Varshni formula, its intensity however decreases with damage while the D-A peak increases considerably. Nitrogen post-etch plasma was shown to improve the band edge peak and decrease the D-A peak. This suggests that the N2 plasma has helped reduce the number of trapped carriers that were participating in the D-A transition and made the D°X transition more active, which reaffirms the N2 post-etch plasma treatment as a good technique to heal the GaN surface, most likely by filling the nitrogen vacancies previously created by etch damage.

Reactive ion etching of Si_2Sb_2Te_5 in CF_4/Ar plasma for a nonvolatile phase-change memory device

Phase change random access memory （PCRAM） is one of the best candidates for next generation non- volatile memory, and phase change SiESbETe5 material is expected to be a promising material for PCRAM. In the fabrication of phase change random access memories, the etching process is a critical step. In this paper, the etching characteristics of Si2Sb2Te5 films were studied with a CF4/Ar gas mixture using a reactive ion etching system. We observed a monotonic decrease in etch rate with decreasing CF4 concentration, meanwhile, Ar concentration went up and smoother etched surfaces were obtained. It proves that CF4 determines the etch rate while Ar plays an im- portant role in defining the smoothness of the etched surface and sidewall edge acuity. Compared with GeESbETe5, it is found that Si2Sb2Te5 has a greater etch rate. Etching characteristics of Si2SbETe5 as a function of power and pressure were also studied. The smoothest surfaces and most vertical sidewalls were achieved using a CF4/Ar gas mixture ratio of 10/40, a background pressure of 40 mTorr, and power of 200 W.

Reactive ion etching of Ti-diffused LiNbO_3 slab waveguides

Reactive ion etching（RIE） of LiNbO_3（LN） in SF_6 plasma atmosphere was studied for optimizing the preparation conditions for LN ridge waveguides.The samples to be etched are Ti-diffused LN slab waveguides overlaid with a chromium film mask that has a Mach-Zehnder interferometer（MZI） array pattern.The experimental results indicate that the LN-etching rate（R_（LN）） and the Cr-etching rate（R_（Cr）） as well as the rate ratio R_（LN）/R_（Cr） increase with either increasing the radio-frequency（RF） power at a given SF_6 flow rate or increasing the SF_6 flow rate at a fixed RF power.The maximum values of R_（LN） = 43.2 nm/min and R_（LN）/R_（Cr） = 3.27 were achieved with 300 W RF power and 40 sccm SF_6 flow.When the SF_6 flow rate exceeds 40 sccm,an increase in the flow rate causes the etching rates and the rate ratio to decrease.The scanning electron microscope images of the LN ridge prepared after～20 min etching show that the ridge height is 680 nm and the sidewall slope angle is about 60°.

Fabrication of High-Density Out-of-Plane Microneedle Arrays with Various Heights and Diverse Cross-Sectional Shapes

Out-of-plane microneedle structures are widely used in various applications such as transcutaneous drug delivery and neural signal recording for brain machine interface.This work presents a novel but simple method to fabricate high-density silicon(Si)microneedle arrays with various heights and diverse cross-sectional shapes depending on photomask pattern designs.The proposed fabrication method is composed of a single photolithography and two subsequent deep reactive ion etching(DRIE)steps.First,a photoresist layer was patterned on a Si substrate to define areas to be etched,which will eventually determine the final location and shape of each individual microneedle.Then,the 1st DRIE step created deep trenches with a highly anisotropic etching of the Si substrate.Subsequently,the photoresist was removed for more isotropic etching;the 2nd DRIE isolated and sharpened microneedles from the predefined trench structures.Depending on diverse photomask designs,the 2nd DRIE formed arrays of microneedles that have various height distributions,as well as diverse cross-sectional shapes across the substrate.With these simple steps,high-aspect ratio microneedles were created in the high density of up to 625 microneedles mm^(-2)on a Si wafer.Insertion tests showed a small force as low as~172μN/microneedle is required for microneedle arrays to penetrate the dura mater of a mouse brain.To demonstrate a feasibility of drug delivery application,we also implemented silk microneedle arrays using molding processes.The fabrication method of the present study is expected to be broadly applicable to create microneedle structures for drug delivery,neuroprosthetic devices,and so on.

Fabrication of Diamond Microstructures by Using Dry and Wet Etching Methods

Diamond films have great potential for micro-electro-mechanical system（MEMS） application.For device realization,precise patterning of diamond films at micrometer scale is indispensable.In this paper,simple and facile methods will be demonstrated for smart patterning of diamond films,in which two etching techniques,i.e.,plasma dry etching and chemical wet etching（including isotropic-etching and anisotropic-etching） have been developed for obtaining diamond microstructures with different morphology demands.Free-standing diamond micro-gears and micro-combs were achieved as examples by using the experimental procedures.It is confirmed that as-designed diamond structures with a straight side wall and a distinct boundary can be fabricated effectively and efficiently by using such methods.

Subtle Variations in Surface Properties of Black Silicon Surfaces Influence the Degree of Bactericidal Efficiency

One of the major challenges faced by the biomedical industry is the development of robust synthetic surfaces that can resist bacterial colonization. Much inspiration has been drawn recently from naturally occurring mechano-bactericidal surfaces such as the wings of cicada(Psaltoda claripennis) and dragonfly(Diplacodes bipunctata) species in fabricating their synthetic analogs. However,the bactericidal activity of nanostructured surfaces is observed in a particular range of parameters reflecting the geometry of nanostructures and surface wettability. Here,several of the nanometer-scale characteristics of black silicon(bSi) surfaces including the density and height of the nanopillars that have the potential to influence the bactericidal efficiency of these nanostructured surfaces have been investigated. The results provide important evidence that minor variations in the nanoarchitecture of substrata can substantially alter their performance as bactericidal surfaces.

Self-powered flexible fingerprint-recognition display based on a triboelectric nanogenerator

In the time of Internet of Things(IoT),alternating current electroluminescence(ACEL)has unique advantages in the fields of smart display and human–computer interaction.However,their reliance on external high-voltage AC power supplies poses challenges in terms of wearability and limits their practical application.This paper proposed an innovative scheme for preparing a feather triboelectric nanogenerator(F-TENG)using recyclable and environmentally friendly material.The highest open-circuit voltage,short-circuit current,and transferred charge of SF6-treated F-TENGs can reach 449 V,63μA,and 152 nC,which enables easy lighting of BaTiO_(3)^(-)doped ACEL devices.Using a human electrical potential,a single-electrode F-TENG is combined with ACEL device for self-powered fingerprint recognition display.These works achieve self-powered flexible wearable ACEL devices,which are not only efficient and portable but also have good application prospects in the human–computer interaction,functional displays,and wearable electronic devices.

Effect of CHF3/Ar Gas Flow Ratio on Self-masking Subwavelength Structures Prepared on Fused Silica Surface

Based on an advanced technology, randomly-aligned subwavelength structures（SWSs） were obtained by a metal-nanodot-induced one-step self-masking reactive-ion-etching process on a fused silica surface. Metal-fluoride（mainly ferrous-fluoride） nanodots induce and gather stable fluorocarbon polymer etching inhibitors in the reactive-ion-etching polymers as masks. Metal fluoride（mainly ferrous fluoride） is produced by the sputtering of argon plasma and the ion-enhanced chemical reaction of metal atoms. With an increase in CHF_3/Ar gas flow ratio, the average height of the SWSs increases, the number of SWSs per specific area increases and then decreases, and the optical transmittance of visible light increases and then decreases. The optimum CHF_3/Ar gas flow ratio for preparing SWSs is 1：5.

Biomimetic Corrugated Silicon Nanocone Arrays for Self-Cleaning Antireflection Coatings

Corrugated silicon nanocone(SiNC)arrays have been fabricated on a silicon wafer by two polystyrene-sphere-monolayer-masked etching steps in order to create high-performance antireflective coatings.The reflectance was reduced from above 35%to less than 0.7%in the range 400-1050 nm,and it remained below 0.5%at incidence angles up to 70°at 632.8 nm for both s-and p-polarized light.The fluorinated corrugated SiNC array surface exhibits superhydrophobic properties with a water contact angle of 164°.

A review:crystalline silicon membranes over sealed cavities for pressure sensors by using silicon migration technology

A silicon pressure sensor is one of the very first MEMS components appearing in the microsystem area.The market for the MEMS pressure sensor is rapidly growing due to consumer electronic applications in recent years. Requirements of the pressure sensors with low cost, low power consumption and high accuracy drive one to develop a novel technology. This paper first overviews the historical development of the absolute pressure sensor briefly. It then reviews the state of the art technology for fabricating crystalline silicon membranes over sealed cavities by using the silicon migration technology in detail. By using only one lithographic step, the membranes defined in lateral and vertical dimensions can be realized by the technology. Finally, applications of MEMS through using the silicon migration technology are summarized.

Fast patterning and dry-etch of SiN_x for high resolution nanoimprint templates

We developed a simplified nanofabrication process for imprint templates by fast speed electron beam lithography（EBL） and a dry etch technique on a SiNx substrate,intended for large area manufacturing.To this end,the highly sensitive chemically amplified resist（CAR）,NEB-22,with negative tone was used.The EBL process first defines the template pattern in NEB-22,which is then directly used as an etching mask in the subsequent reactive ion etching（RIE） on the SiNx to form the desired templates.The properties of both e-beam lithography and dry etch of NEB-22 were carefully studied,indicating significant advantages of this process with some drawbacks compared to when Cr was used as an etching mask.Nevertheless,our results open up a good opportunity to fabricate high resolution imprint templates with the prospect of wafer scale manufacturing.

Fabrication of SiO_2 microdisk optical resonator

The silica microdisk optical resonator which exhibits whispering-gallery-type modes with quality factors of 9.67 x 104 is fabricated with photolithographic techniques. Reactive ion beam etching （RIBE） is used to get the silica disks with photoresist masks on SiO2/Si made by standard ultraviolet （UV） photolithography, and spontaneous silicon etching by XeF2 is used to fabricate the silicon micropillars. This fabrication process can control the microcavity geometry, leading to high experiment repeatability and controllable cavity modes. These characteristics are important for many applications in which the microcavity is necessary, such as the auantum gate.

Echinacoside Protects Against MPP+-Induced Neuronal Apoptosis via ROS/ATF3/CHOP Pathway Regulation

Echinacoside （ECH） is protective in a mouse model of Parkinson＇ s disease （PD） induced by 1-methyl-4- phenylpyridinium ion （MPP＋）. To investigate the mechanisms involved, SH-SYSY neuroblastoma ceils were treated with MPP＋ or a combination of MPP＋ and ECH, and the expression of ATF3 （activating transcription factor 3）, CHOP （C/EBP-homologous protein）, SCNA （synuclein alpha）, and GDNF （glial cell line-derived neurotrophic factor） was assessed. The results showed that ECH significantly improved cell survival by inhibiting the generation of MPP＋-induced reactive oxygen species （ROS）. In addition, ECH suppressed the ROS and MPP＋- induced expression of apoptotic genes （ATF3, CHOP, and SCNA）. ECH markedly decreased the MPP＋-induced cas- pase-3 activity in a dose-dependent manner. ATF3- knockdown also decreased the CHOP and cleaved caspase- 3 levels and inhibited the apoptosis induced by MPP＋. Interestingly, ECH partially restored the GDNF expression that was down-regulated by MPP＋. ECH also improved dopaminergic neuron survival during MPP＋ treatment and protected these neurons against the apoptosis induced by MPTP. Taken together, these data suggest that the ROS/ ATF3/CHOP pathway plays a critical role in mechanisms by which ECH protects against MPP＋-induced apoptosis in PD.

Polymeric 32-channel arrayed waveguide grating multiplexer using fluorinated poly (ether ether ketone)

In wavelength division multiplexing (WDM) systems, arrayed waveguide grating (AWG) multiplexer is a key component. Polymeric AWG multiplexer has recently attracted much attention due to its low cost processing and a potential of integration with other devices. Fluorinated polyether ether ketone (FPEEK) is excellent material for fabrication of optical waveguides due to its low absorption loss at 1.55-μm wavelength and high thermal stability. A 32-channel AWG multiplexer has been designed based on the grating diffraction theory and fabricated using newly synthesized FPEEK. During the fabrication process of the polymer/Si AWG device, spin coating, vaporizing, photolithographic patterning and reactive ion etching (RIE) are used. The AWG multiplexer measurement system is based on a tunable semiconductor laser, an infrared camera and a Peltier-type heater. The device exhibits a wavelength channel spacing of 0.8 nm and a center wavelength of 1548 nm at room temperature.

Self-generating nanogaps for highly effective surface-enhanced Raman spectroscopy

The fabrication of surface enhanced Raman spectroscopy(SERS)substrates with controlled high density hot spots still remains challenging.Herein,we report highly effective SERS substrates containing the self-generating(SG)nanogaps from polystyrene nanosphere monolayer through isotropic plasma etching.The emergence of multimode hot spots,i.e.,metal film over nanosphere(MFON)-like hot spots(closed gaps,0 nm),individual self-aligned hot spots(discrete gaps,>20 nm)and threedimensional(3D)hot spots(nanogaps,1-10 nm),makes the SG SERS substrates superior as compared to the traditional MFON or the well-ordered self-aligned SERS substrates in terms of enhancement,uniformity,and reproducibility.The SG SERS substrates can function as the excellent SERS platforms for trace molecule detection in the practical application fields.

Effect of oxygen terminated surface of boron-doped diamond thin-film electrode on seawater salinity sensing

Tremendous demands for highly sensitive and stable seawater salinometers have motivated intensive research on advanced electrode materials.Boron-doped diamond(BDD)is attractive in terms of its high mechanical stability and chemical inertness,but is usually hindered by its low double-layer capacitance(C_(dl))for seawater salinity detection.Here,inspired by the principle of oxygen-terminated BDD electrode endowing higher C_(dl)than hydrogen-terminated surface,we introduce the oxygen terminated surface by oxygen plasma or reactive ion etch(RIE),and the fabricated oxygen terminated BDD electrodes demonstrate high sensitivity and long-term stability in seawater salinity detection comparing with the hydrogen terminated BDD electrodes.Significantly,the as-fabricated O-BDD-RIE electrodes not only show remarkable enhanced response even better than the commercial platinum black electrodes but also display long-time stability which is weekly verified by continuous monitor for 90 days.The outstanding performance of the oxygen terminated BDD electrodes can be ascribed to the enhancement of C-O surface functional group on C_(dl).In addition,a comprehensive analysis of effective electroactive surface area(EASA)and C_(dl)proves that the surface oxygen is the major factor for the improved C_(dl).In summary,the excellent oxygen terminated BDD electrodes promise potential application in seawater salinity detection.