Electro Mechanical Systems Process Research Articles

A micro packed preconcentrator using ionic liquid coated graphitized carbons for detection of low concentration isoprene

Analysis of volatile organic compounds in the human exhaled mixture is a promising disease screening approach, and isoprene is a typical biomarker for nonalcoholic fatty liver disease in breath diagnosis. However, accurate detection of trace isoprene (ppb) is difficult due to the interfering effect of various gas sensors. In this study, we developed an integrated silicon-based micro preconcentrator (micro-PC) as a pretreatment component of the portable gas chromatography (GC) system. The device was the structure of parallel micro channels with flat dimensions of 20 mm × 10 mm on the silicon substrate, and the total internal empty volume is about 18 μl. The micro electro mechanical system processes were used to fabricate the micro channels and the heating and temperature measuring resistances. The preconcentrator was filled with graphitized carbons with ionic liquids coating as an adsorbent. In the experiments, a GC equipped with a flame ionization detector was used to characterize the preconcentration performance. The micro-PC has a preconcentration factor (PF) value up to 49.8 for 100 ppb isoprene in 5 min adsorption time. Under the same conditions, the PF value of micro-PC using the modified adsorbent was 3.3 times higher than that using the commercial functional material. Besides, the fabricated preconcentrator had excellent desorption efficiency and good humidity resistance. These results indicated that the micro-PC we developed had a potential application in the micro GC system for non-invasive screening of chronic liver related diseases by detecting the trace isoprene.

Raman Scattering Study on the Influence of E-Beam Bombardment on Si Electron Lens.

Microcolumns have a stacked structure composed of an electron emitter, electron lens (source lens), einzel lens, and a deflector manufactured using a micro electro-mechanical system process. The electrons emitted from the tungsten field emitter mostly pass through the aperture holes. However, other electrons fail to pass through because of collisions around the aperture hole. We used Raman scattering measurements and X-ray photoelectron spectroscopy analyses to investigate the influence of electron beam bombardment on a Si electron lens irradiated by acceleration voltages of 0, 20, and 30 keV. We confirmed that the crystallinity was degraded, and carbon-related contamination was detected at the surface and edge of the aperture hole of the Si electron lens after electron bombardment for 24 h. Carbon-related contamination on the surface of the Si electron lens was verified by analyzing the Raman spectra of the carbon-deposited Si substrate using DC sputtering and a carbon rod sample. We report the crystallinity and the origin of the carbon-related contamination of electron Si lenses after electron beam bombardment by non-destructive Raman scattering and XPS analysis methods.

Manufacturing micropatterned collagen scaffolds with chemical-crosslinking for development of biomimetic tissue-engineered oral mucosa

The junction between the epithelium and the underlying connective tissue undulates, constituting of rete ridges, which lack currently available soft tissue constructs. In this study, using a micro electro mechanical systems process and soft lithography, fifteen negative molds, with different dimensions and aspect ratios in grid- and pillar-type configurations, were designed and fabricated to create three-dimensional micropatterns and replicated onto fish-scale type I collagen scaffolds treated with chemical crosslinking. Image analyses showed the micropatterns were well-transferred onto the scaffold surfaces, showing the versatility of our manufacturing system. With the help of rheological test, the collagen scaffold manufactured in this study was confirmed to be an ideal gel and have visco-elastic features. As compared with our previous study, its mechanical and handling properties were improved by chemical cross-linking, which is beneficial for grafting and suturing into the complex structures of oral cavity. Histologic evaluation of a tissue-engineered oral mucosa showed the topographical microstructures of grid-type were well-preserved, rather than pillar-type, a well-stratified epithelial layer was regenerated on all scaffolds and the epithelial rete ridge-like structure was developed. As this three-dimensional microstructure is valuable for maintaining epithelial integrity, our micropatterned collagen scaffolds can be used not only intraorally but extraorally as a graft material for human use.

Microfabrication of multi-layer glassy carbon microstructures through dye-doped negative photoresists

We report on a new technique for microfabrication of multi-layer thick microstructures consisting of a combination of glassy carbon (GC) layers alone, or layers with both GC and negative resist. In this technique, we dope a negative tone pre-cursor polymer of GC structures with a dye that will serve as an ultraviolet (UV) light blocking layer. This allows the doped negative resist layer to act—when needed—as a sacrificial layer which subsequently will enable the patterning of multiple layers of negative resists that can be pyrolyzed and turned in to GC microstructures. In this study, we demonstrate that this method offers a high yield and reliable extension of the classical carbon micro electromechanical systems process to microstructures consisting of multi-layer of GC and a combination of GC and negative resist layers. This batch process, therefore, forms a basis for a high yield and reproducible microfabrication technology for a variety of multiple layers of GC microstructures. In this study we demonstrate: (i) the optimum mixing ratio by-weight of dye and negative resist to be 1:50 (in this case, SU-8); (ii) optimized level of UV exposure needed for the dye-doped SU-8 layer to act as a sacrificial layer (1500 mJ cm−2); and (iii) microfabrication of a variety of thick (>250 µm) multi-layer GC and GC/SU-8 microstructures. The devices fabricated through these techniques include an accelerometer, a micromirror, a string resonator, and a microfluidic chip.

An On‐Chip SiC MEMS Device with Integrated Heating, Sensing, and Microfluidic Cooling Systems

AbstractThere has been increasing interest in electronic systems with integrated microfluidic active cooling modules. However, the failure of 3C‐SiC/Si interface with increasing temperature has prevented the development of 3C‐SiC power electronic devices. Here, all integrated transparent heating, sensing, and cooling systems are developed on a single silicon carbide (SiC) chip for efficient thermal management. SiC nanofilms are grown on a silicon wafer, are transferred to a glass substrate, and then a micro electromechanical system process is employed to fabricate a SiC‐on‐glass system with integrated heaters and temperature sensors. A cooling system is fabricated with microchannel using 3D printing, molding, and plasma assisted bonding. The thermal management of the SiC‐based system shows an excellent capability of heating and detecting temperature as well as effective cooling with an efficiency of from 0.24 to 0.28 and a maximum cooling rate of 0.1 K(µL min−1)−1. The fabrication strategy can be utilized for large production of SiC power nanoelectronics with high efficiency of integrated thermal management systems.

Effects of the Manufacturing Process on the Reliability of the Multilayer Structure in MetalMUMPs Actuators: Residual Stresses and Variation of Design Parameters.

Potential problems induced by the multilayered manufacturing process pose a serious threat to the long-term reliability of MEMSCAP® actuators under in-service thermal cycling. Damage would initiate and propagate in different material layers because of a large mismatch of their thermal expansions. In this research, residual stresses and variations of design parameters induced by metal multi-user micro electromechanical system processes (MetalMUMPs) were examined to evaluate their effects on the thermal fatigue lifetime of the multilayer structure and, thus, to improve MEMSCAP® design. Since testing in such micro internal structure is difficult to conduct and traditional testing schemes are destructive, a numerical subdomain method based on a finite element technique was employed. Thermomechanical deformation from metal to insulator layers under in-service temperature cycling (obtained from the multiphysics model of the entire actuator, which was validated by experimental and specified analytical solutions) was accurately estimated to define failures with a significant efficiency and feasibility. Simulation results showed that critical failure modes included interface delamination, plastic deformation, micro cracking, and thermal fatigue, similarly to what was concluded in the MEMSCAP® technical report.

Microfabrication of a scanning probe with NV centers in a selectively grown diamond thin film through a xenon difluoride etching process

A scanning probe with nitrogen vacancy (NV) centers in diamond thin film was fabricated via a standard micro/nano electromechanical system process. The diamond thin film was selectively grown by microwave plasma enhanced chemical vapor deposition on a partially nucleated silicon surface. NV centers are embedded during the diamond growth with a pure nitrogen gas flow to the growth chamber. The existence of NV centers in the diamond thin film was confirmed by photoluminescence measurements. In addition, we found that a xenon difluoride (XeF2) etching process and anneal treatment have an influence on the existence of NV centers in the diamond. The fabricated scanning probe with NV centers in diamond thin film can be used as a magnetic scanning sensor. It is anticipated that the alternative method of selectively growing diamond thin film provides various diamond structures in diverse applications.

Fabrication of piezoelectric vibration energy harvester using coatable PolyVinylidene DiFluoride and its characterisation

A cantilever-type vibration energy harvester (VEH) made of PolyVinylidene DiFluoride (PVDF) was fabricated and characterised. PVDF is one of polymer piezoelectric material, which is more flexible than ceramic-based piezoelectric materials such as lead zirconate titanate. Since PVDF dissolves in organic solvent, it is coatable on substrate or parts, making it compatible with micro electro mechanical systems process. The fabrication process of VEH is as follows: a PVDF film (thickness: 30 µm) was coated on a phosphor bronze rectangular plate (length: 35 mm, width: 15 mm, thickness: 0.1 mm) by bar-coating method, followed by polarisation by corona discharge method. Aluminium top electrode (length: 30 mm, width: 10 mm, thickness: 0.3 μm) was deposited on the PVDF film by DC sputtering. One end of the plate was clamped by a fixture to form a cantilever, the length of which is 25 mm. Finally, a proof mass (m = 0.2 g) was attached to the free end of cantilever. Output power P at resonant frequency (= 55 Hz) was measured as a function of load resistance R, in which acceleration was set to 17 m/s2. Maximum output of 4.3 µW was achieved at R = 2.1 MΩ, which is not inferior to those of reported VEHs using ceramic piezoelectric materials.

A novel self-sensing technique for tapping-mode atomic force microscopy

This work proposes a novel self-sensing tapping-mode atomic force microscopy operation utilizing charge measurement. A microcantilever coated with a single piezoelectric layer is simultaneously used for actuation and deflection sensing. The cantilever can be batch fabricated with existing micro electro mechanical system processes. The setup enables the omission of the optical beam deflection technique which is commonly used to measure the cantilever oscillation amplitude. Due to the high amount of capacitive feedthrough in the measured charge signal, a feedforward control technique is employed to increase the dynamic range from less than 1 dB to approximately 35 dB. Experiments show that the conditioned charge signal achieves excellent signal-to-noise ratio and can therefore be used as a feedback signal for atomic force microscopy imaging.

An innovative tri-axes micro-power receiver for inductively wireless power transmission

An innovative tri-axes micro-power receiver is proposed and studied for wireless magnetic energy transmission. The tri-axes micro-power receiver mainly consists of two sets of three-dimensional micro-solenoids and one set of planar micro-coils in which individual iron core is all embedded. The three sets of micro-coils/micro-solenoids are designed to be orthogonal to each other. Therefore, no matter which direction the input magnetic flux is present along, the supplied magnetic energy can be harvested and transformed into electric power by the proposed micro-power receiver in wireless sense. Not only the dead zone of receiving power is greatly reduced, but also transformation efficacy of magnetic energy into electric power can be much enhanced. By Governing Equations Analysis (GEA), based on Biot-Savart law and Faraday's law, the mathematical description upon power transmission from transmitter to receiver is established. The estimation error on power transmission by commercial software, Ansoft Maxwell, based on finite element method, is revealed, in comparison to GEA method. Moreover, the design parameters of tri-axes micro-receiver are examined and verified for follow-up fabrication and experiments. Particularly for the micro electro mechanical systems process, the isotropic etching technique is employed to micro-machine the inverse-trapezoid fillister for solenoid at receiver, so that the copper wire can be successfully electroplated. Therefore, the adhesion between micro-coils and fillister is hence much enhanced as well.

High performance read-out IC design for IR image sensor applications

In this paper, high performance read-out integrated circuits (ROIC) for infrared (IR) image sensor applications is proposed. Because an uncooled microbolometer image sensor, used in an IR image sensor, is made by a micro electro mechanical systems process, the resistance of bolometer by each process does not appear same value under same temperature condition. This resistance variation generates a different output signal for same input by each chip. In order to improve on these drawbacks, a ROIC, which compensates for the error described above, was designed. Instead of a single input mode, a differential input mode ROIC was proposed and thus, a new circuit structure was proposed. Using results from a computer simulation, improvements such as that the effect of the process error was decreased 10---12% without an additional compensation circuit was found. Based on the simulation results, a prototype device including a ROIC and a micro bolometer with 16 × 16 cell arrays was fabricated and characterized.

Fabrication and characterization of VO2 thin films by direct current facing targets magnetron sputtering and low temperature oxidation

Low valence vanadium oxide(VO2−x ) thin films were prepared on SiO2/Si substrates at room temperature by direct current facing targets reactive magnetron sputtering, and then processed through rapid thermal annealing. The effects of the annealing on the structure and phase transition property of VO2 were discussed. X-ray photoelectron spectroscopy, X-ray diffraction technique and Fourier transform infrared spectroscopy were employed to study the phase composition and structure of the thin films. The resistance-temperature property was measured. The results show that VO2 thin film is obtained after annealed at 320 °C for 3 h, its phase transition temperature is 56 °C, and the resistance changes by more than 2 orders. The vanadium oxide thin films are applicable in thermochromic smart windows, and the deposition and annealing process is compatible with micro electromechanical system process.

The fabrication and application of Zernike electrostatic phase plate

The Zernike electrostatic phase plate (ZEPP) consisting of three ring electrodes and two insulating rings has been fabricated using Micro Electro-Mechanical System processes. The electrostatic field produced in the phase plate was measured by electrostatic force microscopy. The electrostatic field and focal length of the phase plate is calculated using electron optics principles. The comparison of the experimental electrostatic field and the theoretical calculated is discussed. Finally, we report the application of ZEPP to enhance contrast of the SiON(x)/SiO(2) interface in an NMOS semiconductor device. The quantitative analysis of the contrast enhancement versus the applied bias is discussed in detail.