Silicon nanowire formed via shallow anisotropic etching Si-ash-trimming for specific DNA and electrochemical detection

A functionalized silicon nanowire field-effect transistor （SiNW FET） was fabricated to detect single molecules in the pM range to detect disease at the early stage with a sensitive, robust, and inexpensive method with the ability to provide specific and reliable data. The device was designed and fabricated by indented ash trimming via shallow anisotropic etching. The approach is a simple and low-cost technique that is compatible with the current commercial semiconductor standard CMOS process without an expensive deep reactive ion etcher. Specific electric changes were observed for DNA sensing when the nanowire surface was modified with a complementary captured DNA probe and target DNA through an organic linker （--OCH2CH3） using organofunctional alkoxysilanes （3-aminopropyl） triethoxysilane （APTES）. With this surface modification, a single specific target molecule can be detected. The simplicity of the sensing domain makes it feasible to miniaturize it for the development of a cancer detection kit, facilitating its use in both clinical and non-clinical environments to allow non-expert interpretation. With its novel electric response and potential for mass commercial fabrication, this biosensor can be developed to become a portable/point of care biosensor for both field and diagnostic applications.

The Effects of Chemical (isotropic) and Anisotropic Etching Processes on the Roughening of Nanocomposite Substrates

Simulation results of roughening of nanocomposite materials during both isotropic and anisotropic etching processes based on the level set method are presented. It is clearly shown that the presence of two phases with different etching rates affects the development of surface roughness and that some roughness characteristics obey simple scaling laws. In addition, certain scaling laws that describe the time dependence of the root mean square （rms） roughness w for various etching processes and different characteristics of the nanocomposite materials are determined.

Anisotropic etching of 2D layered materials

Two-dimensional(2D)layered materials with unique physicochemical properties,such as graphene,transition metal dichalcogenides,and hexagonal boron nitride,have shown considerable potential in the electrical and electronics industries as well as society.To realize the practical applications of 2D materials,the size,shape,and edge structures must be refined.Etching is a critical processing step in the semiconducting industry and its potential as an efficient approach for fabricating diverse nanostructures of 2D materials has been demonstrated,broadening their applications in the field of nanoelectronics.In this paper,we present an overview of recent advances in anisotropic etching of various 2D materials.Anisotropic etching and the associated mechanisms are discussed in context of the synthesis,processing,and characterization of 2D materials.An overview of the applications of anisotropic etched 2D materials is provided.Finally,the challenges and future opportunities for anisotropic etching of 2D materials are discussed.

Multi-stage anisotropic etching of two-dimensional heterostructures

Regarding the reverse process of materials growth,etching has been widely concerned to indirectly probe the growth kinetics,offering an avenue in governing the growth of two-dimensional(2D)materials.In this work,interface-driven anisotropic etching mode is demonstrated for the first time to be generally applied to 2D heterostructures.It is shown that the typical in-plane graphene and hexagonal boron nitride(h-BN)heterostructures follow a multi-stage etching behavior initiated first along the interfacial region between the two materials and then along edges of neighboring h-BN flakes and finally along central edges of hBN.By accurately tuning etching conditions in the chemical vapor deposition process,series of etched 2D heterostructure patterns are controllably produced.Furthermore,scaled formation of graphene and h-BN heterostructures arrays has been realized with full assist of as-proposed etching mechanism,offering a direct top-down method to make 2D orientated heterostructures with order and complexity.Detection of interface-driven multi-staged anisotropic etching mode will shed light on understanding growth mechanism and further expanding wide applications of 2D heterostructures.

A novel method for generating a rectangular convex corner compensation structure in an anisotropic etching process

Detailed characteristics of three classical rectangular convex corner compensation structures on（100） silicon substrates have been investigated, and their common design steps are summarized.By combining the basic method of a silicon wet anisotropic etching process, a general method of generating compensation structures for a rectangular convex corner is put forward.This calls for the following two steps：define the topological field and fit some borderlines together into practical compensation patterns.The rules, which must be obeyed during this process, are summarized.By introducing this method, some novel compensation patterns for rectangular convex corner structures are created on both（100） and（110） substrates, and finally simulation results are given to prove this new method＇s validity and applicability.

A Novel Silicon Etching Method Using Vapor of Tetramethylammonium Hydroxide Solution

Silicon bulk etching is an important part of micro-electro-mechanical system(MEMS) technology. In this work, a novel etching method is proposed based on the vapor from tetramethylammonium hydroxide(TMAH) solution heated up to boiling point. The monocrystalline silicon wafer is positioned over the solution surface and can be anisotropically etched by the produced vapor. This etching method does not rely on the expensive vacuum equipment used in dry etching. Meanwhile, it presents several advantages like low roughness, high etching rate and high uniformity compared with the conventional wet etching methods. The etching rate and roughness can reach 2.13 μm/min and 1.02 nm, respectively. Furthermore,the diaphragm structure and Al-based pattern on the non-etched side of wafer can maintain intact without any damage during the back-cavity fabrication. Finally, an etching mechanism has been proposed to illustrate the observed experimental phenomenon. It is suggested that there is a water thin film on the etched surface during the solution evaporation. It is in this water layer that the ionization and etching reaction of TMAH proceed, facilitating the desorption of hydrogen bubble and the enhancement of molecular exchange rate. This new etching method is of great significance in the low-cost and high-quality micro-electromechanical system industrial fabrication.

Study on atomic layer etching of Si in inductively coupled Ar/Cl_2 plasmas driven by tailored bias waveforms

Plasma atomic layer etching is proposed to attain layer-by-layer etching, as it has atomic-scale resolution, and can etch monolayer materials. In the etching process, ion energy and angular distributions（IEADs） bombarding the wafer placed on the substrate play a critical role in trench profile evolution, thus importantly flexibly controlling IEADs in the process. Tailored bias voltage waveform is an advisable method to modulate the IEADs effectively, and then improve the trench profile. In this paper, a multi-scale model, coupling the reaction chamber model,sheath model, and trench model, is used to research the effects of bias waveforms on the atomic layer etching of Si in Ar/Cl2 inductively coupled plasmas. Results show that different discharge parameters, such as pressure and radio-frequency power influence the trench evolution progress with bias waveforms synergistically. Tailored bias waveforms can provide nearly monoenergetic ions, thereby obtaining more anisotropic trench profile.？？？

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.

Fabrication-Technology Research of New Type Silicon Magnetic-Sensitive Transistor

This paper mainly describes a research of fabrication-technology of silicon magnetic-sensitive transistor (SMST) with rectangle-plank-cubic structure fabricated on silicon wafer by MEMS technique.An experiment research on basic characteristic of the silicon magnetic-sensitive transistor was done.Anisotropic etching and reliable technique project were provided and applied in order to fabricate SMST with rectangle-plank-cubic construction.This means that a new kind of fabrication technology for silicon magnetic-sensitive transistor was provided.The result shows that the technique can be not only compatible with IC technology but also integrated easily,and has a wide application field.

Fabrication of Silicon Crystal-Facet-Dependent Nanostructures by Electron-Beam Lithography

Silicon crystal-facet-dependent nanostructures have been successfully fabricated on a （100）-oriented silicon-oninsulator wafer using electron-beam lithography and the silicon anisotropic wet etching technique. This technique takes advantage of the large difference in etching properties for different crystallographic planes in alkaline solution. The minimum size of the trapezoidal top for those Si nanostructures can be reduced to less than 10nm. Scanning electron microscopy （SEM） and atomic force microscopy （AFM） observations indicate that the etched nanostructures have controllable shapes and smooth surfaces.

Direct visualization of structural defects in 2D semiconductors

Direct visualization of the structural defects in two-dimensional(2D)semiconductors at a large scale plays a significant role in understanding their electrical/optical/magnetic properties,but is challenging.Although traditional atomic resolution imaging techniques,such as transmission electron microscopy and scanning tunneling microscopy,can directly image the structural defects,they provide only local-scale information and require complex setups.Here,we develop a simple,non-invasive wet etching method to directly visualize the structural defects in 2D semiconductors at a large scale,including both point defects and grain boundaries.Utilizing this method,we extract successfully the defects density in several different types of monolayer molybdenum disulfide samples,providing key insights into the device functions.Furthermore,the etching method we developed is anisotropic and tunable,opening up opportunities to obtain exotic edge states on demand.

Effects of etching conditions on surface morphology of periodic inverted trapezoidal patterned Si(100) substrate

In this paper,the anisotropic etching process of Si(100) wafers in tetramethyl ammonium hydroxide(TMAH) solution with isopropyl alcohol(IPA) is investigated in detail. An inverted trapezoidal pattern is developed. A series of experiments are performed by changing TMAH concentration,IPA concentration,etching temperature and etching time. The structure of inverted trapezoidal patterns and roughness of the bottom surface are characterized by scanning electron microscopy(SEM) and atomic force microscopy(AFM). The results show that with TMAH concentration increases,the roughness of bottom surface will decrease. The addition of IPA into TMAH solution improves the morphology of the bottom surface significantly. Low temperature is beneficial to get a smooth bottom surface. Furthermore,etching time can change the bottom surface roughness. A model is proposed to explain the etching processes. The hillock area ratio of the bottom surface has the same tendency as the etching area ratio. Finally,smooth silicon inverted trapezoidal patterns are obtained for epitaxial growth of Ga N-based light emitting diode(LED) devices.

Lithography-independent and large scale fabrication of a metal electrode nanogap

A lithography-independent and wafer scale method to fabricate a metal nanogap structure is demonstrated. Polysilicon was first dry etched using photoresist （PR） as the etch mask patterned by photolithography. Then, by depositing conformal SiO2 on the polysilicon pattern, etching back SiO2 anisotropically in the perpendicular direction and removing the polysilicon with KOH, a sacrificial SiO2 spacer was obtained. Finally, after metal evaporation and lifting-off of the SiO2 spacer, an 82 nm metal-gap structure was achieved. The size of the nanogap is not determined by the photolithography, but by the thickness of the SiO2. The method reported in this paper is compatible with modern semiconductor technology and can be used in mass production.

Integrated ionic sieving channels from engineering ordered monolayer two-dimensional crystallite structures

Atomically thin solid-state channels enabling selective molecular transport could potentially be used in a variety of separation and energy conversion applications.The density of channels,their height,distance and edge structure are the key factors that dramatically impact the selective transport performance.However,such channels with small constrictions and atomic precision have been limited to proof-ofconcept demonstrations based on microscale two-dimensional(2D)crystal stripes.Here,we report the engineering of highly ordered,scalable monolayer graphene crystallite arrays by chemical vapor deposition(CVD)method with a modified anisotropic etching approach.The size,shape,distance and edge structure of the graphene crystallite arrays in a large area could be delicately controlled through tailoring the synthetic parameters.This array structure can act as pillars to prop up a smooth single-crystal graphene film,and the fabricated integrated angstrom-size(3.4A)channels allow water transport but exclude hydrated ions,demonstrating potential in selective ionic sieving and nanofiltration practice.

Resonant pitch and roll silicon gyroscopes with sub-micron-gap slanted electrodes:Breaking the barrier toward high-performance monolithic inertial measurement units

This paper presents the design,fabrication,and characterization of a novel high quality factor(Q)resonant pitch/roll gyroscope implemented in a 40μm(100)silicon-on-insulator(SOI)substrate without using the deep reactive-ion etching(DRIE)process.The featured silicon gyroscope has a mode-matched operating frequency of 200 kHz and is the first out-of-plane pitch/roll gyroscope with electrostatic quadrature tuning capability to fully compensate for fabrication non-idealities and variation in SOI thickness.The quadrature tuning is enabled by slanted electrodes with sub-micron capacitive gaps along the(111)plane created by an anisotropic wet etching.The quadrature cancellation enables a 20-fold improvement in the scale factor for a typical fabricated device.Noise measurement of quadrature-cancelled mode-matched devices shows an angle random walk(ARW)of 0.63°√h^(−1) and a bias instability of 37.7°h^(−1),partially limited by the noise of the interface electronics.The elimination of silicon DRIE in the anisotropically wet-etched gyroscope improves the gyroscope robustness against the process variation and reduces the fabrication costs.The use of a slanted electrode for quadrature tuning demonstrates an effective path to reach high-performance in future pitch and roll gyroscope designs for the implementation of single-chip high-precision inertial measurement units(IMUs).