Micro-fabrication of ceramics:Additive manufacturing and conventional technologies

Ceramic materials are increasingly used in micro-electro-mechanical systems(MEMS)as they offer many advantages such as high-temperature resistance,high wear resistance,low density,and favourable mechanical and chemical properties at elevated temperature.However,with the emerging of additive manufacturing,the use of ceramics for functional and structural MEMS raises new opportunities and challenges.This paper provides an extensive review of the manufacturing processes used for ceramic-based MEMS,including additive and conventional manufacturing technologies.The review covers the micro-fabrication techniques of ceramics with the focus on their operating principles,main features,and processed materials.Challenges that need to be addressed in applying additive technologies in MEMS include ceramic printing on wafers,post-processing at the micro-level,resolution,and quality control.The paper also sheds light on the new possibilities of ceramic additive micro-fabrication and their potential applications,which indicates a promising future.

Features of micro-fabric and the genetic study of Triassic deep polyhalite in the Guang'an area, central Sichuan Basin

It is an accepted fact that the main solid phase support for potassium in the Sichuan Basin is polyhalite [K2MgCa2(SO4)4·2H2O] rather than sylvineis (KCl) (Gong DX et al.,2015).The mineral types,occurrence characteristics and metasomatism of the polyhalite bearing ore-bed were identified and the origin of the polyhalite was discussed.The polyhalite samples were obtained from the core of Z12,located in Dalong Village,Guang'an City of central Sichuan.The sampling depths were 2974 m (s-1),3023 m (s-2) and 3106 m (s-3).The microbeam analysis of back-scattering images was carried out using a Shimadzu EPMA-1720 Series electron probe micro-analyzer,supplemented by a quantitative spectrum analysis that determined the mineral types.

Novel Resonant Accelerometer with Micro Leverage Fabricated by MEMS Technology

For the purpose of improving the precision of the inertial guidance system,it is necessary to enhance the accuracy of the accelerometer.Combining the micro-fabrication processes with resonant sensor technology,a high-resolution inertial-grade novel micro resonant accelerometer is studied.Based on the detecting theory of the resonant sensors,the accelerometer is designed,fabricated,and tested.The accelerometer consists of one proofmass,two micro leverages and two double-ended-tuning-fork （DETF） resonators.The sensing principle of this accelerometer is based on that the natural frequency of the DETF resonator shifts with its axial load which is caused by inertial force.The push-pull configuration of the DETF is for temperature compensation.The two-stage micro leverage mechanisms are employed to amplify the force and increase the sensitivity of the accelerometer.The micro leverage and the resonator are modeled for static analysis and nonlinear modal analysis via theory method and finite element method （FEM）,respectively.The geometrical parameters of them are optimized.The amplification factor of the leverage is 102,and the sensitivity of the resonator on theory is about 62 Hz/g.The samples of the accelerometer are fabricated with deep reactive ion etching （DRIE） technology which can get a high-aspect ratio structure for contributing a greater sensing-capacitance.The measuring results of the samples by scanning electron microscopy （SEM） show that the process is feasible,because of the complete structure,the sound combs and micro leverages,and the acceptable errors.The frequency of the resonator and the sensitivity of the accelerometer are tested via printed circuit board （PCB）,respectively.The result of the test shows that the frequency of the push-resonator is about 54 530 Hz and the sensitivity of the accelerometer is about 55 Hz/g.The amplification factor of the leverage is calculated more accurately because the coupling of the two stages leverage is considered during derivation of the analysis formula.In addition,the novel differential structure of the accelerometer can greatly improve the sensitivity of the accelerometers.

Fabrication and characterization of ultra-low noise narrow and wide band Josephson parametric amplifiers

We have fabricated two types of lumped-element Josephson parameter amplifiers（JPAs） by using a multilayer microfabrication process involving wet etching of Al films. The first type is a narrow band JPA which shows typical gain above14 dB in a bandwidth around 35 MHz. The second type is a wideband JPA which is coupled to an input 50Ω transmission line via an impedance transformer that changes the impedance from about 15 Ω on the non-linear resonator side to 50 Ωon the input transmission line side. The wideband JPA could operate in a 200 MHz range with a gain higher than 14 d B.The amplifiers were used for superconducting qubit readout. The results showed that the signal to noise ratio and hence the readout fidelity were improved significantly.

Efficiency improvement by using metal–insulator‑semiconductor structure in InGaN/GaN micro‑light‑emitting diodes

InGaN/GaN micro-light-emitting diodes(micro-LEDs)with a metal–insulator-semiconductor(MIS)structure on the sidewall are proposed to improve efficiency.In this MIS structure,a sidewall electrode is deposited on the insulating layer-coated sidewall of the device mesa between a cathode on the bottom and an anode on the top.Electroluminescence(EL)measurements of fabricated devices with a mesa diameter of 10μm show that the application of negative biases on the sidewall electrode can increase the device external quantum efficiency(EQE).In contrast,the application of positive biases can decrease the EQE.The band structure analysis reveals that the EQE is impacted because the application of sidewall electric fields manipulates the local surface electron density along the mesa sidewall and thus controls surface Shockley–Read–Hall(SRH)recombination.Two suggested strategies,reducing insulator layer thickness and exploring alternative materials,can be implemented to further improve the EQE of MIS micro-LEDs in future fabrication.

Additive direct-write microfabrication for MEMS： A review

Direct-write additive manufacturing refers to a rich and growing repertoire of well-established fabrication techniques that builds solid objects directly from compu- ter-generated solid models without elaborate intermediate fabrication steps. At the macroscale, direct-write techni- ques such as stereolithography, selective laser sintering, fused deposition modeling ink-jet printing, and laminated object manufacturing have significantly reduced concept- to-product lead time, enabled complex geometries, and importantly, has led to the renaissance in fabrication known as the maker movement. The technological premises of all direct-write additive manufacturing are identical--converting computer generated three-dimen- sional models into layers of two-dimensional planes or slices, which are then reconstructed sequentially into three- dimensional solid objects in key differences between the a layer-by-layer format. The various additive manufactur- ing techniques are the means of creating the finished layers and the ancillary processes that accompany them. While still at its infancy, direct-write additive manufacturing techniques at the microscale have the potential to significantly lower the barrier-of-entry--in terms of cost, time and training--for the prototyping and fabrication of MEMS parts that have larger dimensions, high aspect ratios, and complex shapes. In recent years, significant advancements in materials chemistry, laser technology, heat and fluid modeling, and control systems have enabled additive manufacturing to achieve higher resolutions at the micrometer and nanometer length scales to be a viable technology for MEMS fabrication. Compared to traditional MEMS processes that rely heavily on expensive equip- ment and time-consuming steps, direct-write additive manufacturing techniques allow for rapid design-to- prototype realization by limiting or circumventing the need for cleanrooms, photolithography and extensive training. With current direct-write additive manufacturingtechnologies, it is possible to fabricate unsophisticated micrometer scale structures at adequate resolutions and precisions using materials that range from polymers, metals, ceramics, to composites. In both academia and industry, direct-write additive manufacturing offers extra- ordinary promises to revolutionize research and develop- ment in microfabrication and MEMS technologies. Importantly, direct-write additive manufacturing could appreciably augment current MEMS fabrication technologies, enable faster design-to-product cycle, empower new paradigms in MEMS designs, and critically, encourage wider participation in MEMS research at institutions or for individuals with limited or no access to cleanroom facilities. This article aims to provide a limited review of the current landscape of direct-write additive manufacturing techniques that are potentially applicable for MEMS microfabrication.

Preparation of patterned SiC and SiCN microstructures

Patterned SiC and SiCN microstructures were successfully fabricated on the silicon substrates by using polydimethylsiloxane (PDMS) elastometric stamp as template, polycarbosilane (PCS) and polysilazane (PSZ) as preceramic polymers. The preparing process was followed by precursor infiltration, the curing of the precursor, demolding of the template and pyrolysis of the cured preceramic polymer pattern. It shows that the dimen- sions of the ceramic patterns can be tailored by using the PDMS molds with different di- mensions. The produced ceramic microstructures can be potentially applied in high tem- perature and high pressure environments due to the advanced properties of the SiC and SiCN ceramics.

A new series of two-photon polymerization initiators:Synthesis and nonlinear optical properties

Four photopolymerization initiators with D-π-D (D,donor; π,conjugation system) structure have been synthesized by solvent-free reaction and characterized by 1H NMR spectroscopy,IR and elemental analysis. The one-photon and two-photon excited fluorescence have been investigated in different solvents. Experimental results of the one-photon and two-photon absorption cross sections show different trends in OPA and TPA ability with different substitution groups in donor units.

A tassel-type multilayer flexible probe for invasive neural recording

Invasive neural probes are one of the most critical components in the intracortical neural signal recording system.However,they can cause brain damage and tissue response during and after implantation.Thus,neural probes with high flexibility,biocompatibility,and simple implantation methods are required in brain research.Here we present a novel approach to fabricating a multilayer flexible tassel-type neural probe using low-cost maskless laser direct-write lithog-raphy,combined with straightforward release and assembly methods to prepare a whole implantation system.The probe has 32 recording electrodes with an area of 8×8μm^(2),arranged into two rows of different depths and 16 separated shanks,aiming at the neural signal recording in an extensive range.Polyimide and gold are used as the insulating and conductive layers,respectively.With the help of a polyethylene glycol(PEG)coating,the tassel structure was mechanically enhanced for successful implantation,and our morphology characterization showed that the diameter of the coated probe was less than 50μm.Mechanical property tests also proved that it had the necessary stiffness for brain implantation.Afterwards,electrochemical tests were carried out,which showed that the probe had a rather low impedance after a simple gold electroplating.Finally,in vivo experiments demonstrated our probe can be successfully used in neural recording.