Anisotropic Wet Etching Technique Research Articles

A miniature confocal Raman probe for endoscopic use

Raman spectroscopy is a powerful tool for studying biochemical changes in the human body. We describe a miniature, confocal fibre optic probe intended to fit within the instrument channel of a standard medical endoscope. This probe has been optimized for the study of the carcinogenesis process of oesophageal malignancy. The optical design and fabrication of this probe is described including the anisotropic wet etching technique used to make silicon motherboards and jigs. Example spectra of PTFE reference samples are shown. Spectra with acquisition times as low as 2 s from resected oesophageal tissue are presented showing identifiable biochemical changes from various pathologies.

Nanogap biosensors for electrical and label-free detection of biomolecular interactions

We demonstrate nanogap biosensors for electrical and label-free detection of biomolecularinteractions. Parallel fabrication of nanometer distance gaps has been achieved using asilicon anisotropic wet etching technique on a silicon-on-insulator (SOI) wafer with a finelycontrollable silicon device layer. Since silicon anisotropic wet etching resulted in atrapezoid-shaped structure whose end became narrower during the etching, the nanogapstructure was simply fabricated on the device layer of a SOI wafer. The nanogap deviceswere individually addressable and a gap size of less than 60 nm was obtained. Wedemonstrate that the nanogap biosensors can electrically detect biomolecular interactionssuch as biotin/streptavidin and antigen/antibody pairs. The nanogap devices show acurrent increase when the proteins are bound to the surface. The current increasesproportionally depending upon the concentrations of the molecules in the range of 100 fg ml−1–100 ng ml−1 at 1 V bias. It is expected that the nanogap developed here could be a highly sensitivebiosensor platform for label-free detection of biomolecular interactions.

재순환 영역이 존재하는 마이크로 혼합기

This paper describes enhancement of the mixing efficiency of a multilamination micro mixer by adding a number of recirculation zones downstream of the mixing zone. Numerical simulation was employed to estimate the mixing efficiency and the pressure drop under various conditions. Numerical results indicated that recirculation micro mixer brought about not only the increase of the mixing efficiency but also the decrease of the pressure drop. Micro mixers were fabricated using photosensitive glass by anisotropic wet etching technique. The width and height of the micro channel were and , respectively. The performance of micro mixer was measured using color intensity variation of the fluid. Except for extremely low Re below 40, the recirculation micro mixer of the present study showed improved mixing. And the enhancement of the mixing increased as Re rose. When Re increased beyond 400, more than 90% of the mixing was observed in the experiment.

Fabrication of suspended GaN microstructures using GaN-on-patterned-silicon (GPS) technique

We demonstrate a technique for fabricating suspended gallium nitride (GaN) microstructures without direct etching of GaN. The process combines a selective area growth of GaN-on-patterned-silicon substrate (GPS) and a subsequent sacrificial wet etching of the silicon under the GaN structures. Both anisotropic and isotropic wet etching techniques are used to carry out the sacrificial etching. The pattern-dependent lateral growth property of GaN growth is also discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A PZT insulin pump integrated with a silicon microneedle array for transdermal drug delivery

Many of the compounds in drugs cannot be effectively delivered using current drug delivery techniques (e.g., pills and injections). Transdermal delivery is an attractive alternative, but it is limited by the extremely low permeability of the skin. As the primary barrier to transport is located in the upper tissue, Micro-Electro-Mechanical-System (MEMS) technology provides novel means, such as microneedle array and PZT pump, in order to increase permeability of human skin with efficiency, safety and painless delivery, and to decrease the size of the pump. Microneedle array has many advantages, including minimal trauma at penetration site because of the small size of the needle, free from condition limitations, painless drug delivery, and precise control of penetration depth. These will promote the development of biomedical sciences and technology and make medical devices more humanized. So far, most of the insulin pumps being used are mechanical pumps. We present the first development of this novel technology, which can assemble the PZT pump and the microneedle array together for diabetes mellitus. The microneedle array based on a flexible substrate can be mounted on non-planar surface or even on flexible objects such as a human fingers and arms. The PZT pump can pump the much more precision drug accurately than mechanical pump and the overall size is much smaller than those mechanical pumps. The hollow wall straight microneedle array is fabricated on a flexible silicon substrate by inductively coupled plasma (ICP) and anisotropic wet etching techniques. The fabricated hollow microneedles are 200 μm in length and 30 μm in diameter. The microneedle array, which is built with on-board fluid pumps, has potential applications in the chemical and biomedical fields for localized chemical analysis, programmable drug-delivery systems, and very small, precise fluids sampling. The microneedle array has been installed in an insulin pump for demonstration and a leak free packaging is introduced.

GaN-on-patterned-silicon (GPS) technique for fabrication of GaN-based MEMS

A method for fabricating suspended gallium nitride (GaN) structures for microelectromechanical systems (MEMS) without direct etching of GaN is demonstrated. The process combines a selective area growth of GaN-on-patterned-silicon-substrate (GPS) and a subsequent sacrificial wet etching of the silicon under the GaN structures. Both anisotropic and isotropic wet etching techniques are used to carry out the sacrificial etching. The experimental results show that the GPS–MEMS technique can be used to batch-fabricate various GaN-based MEMS devices with common silicon micromachining equipments.

Research progresses of SOI optical waveguide devices and integrated optical switch matrix

SOI (silicon-on-insulator) is a new material with a lot of important performances such as large index difference, low transmission loss. Fabrication processes for SOI based optoelectronic devices are compatible with conventional IC processes. Having the potential of OEIC monolithic integration, SOI based optoelectronic devices have shown many good characteristics and become more and more attractive recently. In this paper, the recent progresses of SOI waveguide devices in our research group are presented. By highly effective numerical simulation, the single mode conditions for SOI rib waveguides with rectangular and trapezoidal cross-section were accurately investigated. Using both chemical anisotropic wet etching and plasma dry etching techniques, SOI single mode rib waveguide, MMI coupler, VOA (variable optical attenuator), 2 × 2 thermal-optical switch were successfully designed and fabricated. Based on these, 4 × 4 and 8 × 8 SOI optical waveguide integrated switch matrixes are demonstrated for the first time.

CMOS-Compatible Micromachined Edge-Suspended Spiral Inductors With High Q-Factors and Self-Resonance Frequencies

This paper reports a new category of high-Q edge-suspended inductors (ESI) that are fabricated using CMOS-compatible micromachining techniques. This structure was designed based on the concept that the current was crowded at the edges of the conducting metal wires at high frequencies due to the proximity effect. The substrate coupling and loss can be effectively suppressed by removing the silicon around and underneath the edges of the signal lines. Different from the conventional air-suspended inductors that have the inductors built on membranes or totally suspended in the air, the edge-suspended structures have the silicon underneath the center of the metal lines as the strong mechanical supports. The ESIs are fabricated using a combination of deep dry etching and anisotropic wet etching techniques that are compatible with CMOS process. For a three-turn 4.5-nH inductor, a 70% increase (from 6.8 to 11.7) in maximum Q-factor and a 57% increase (from 9.1 to 14.3 GHz) in self-resonance frequency were obtained with a 11-/spl mu/m suspended edge in 25-/spl mu/m-wide lines.

Silicon-based coupling platform for optical fiber switching in free space

This paper presents the novel concept of a silicon-based coupling platform integrated with an electrostatic-driven out-of-plane optical switch, a self-parking framework, a flat-topped mesa, a v-groove and a microball lens array. The electrostatic-driven out-of-plane optical switch consists of a vertical mirror on a suspension polyimide diaphragm. It can reduce the large motion space required in in-plane optical switches. The method of corner compensation with the help of IntelliCAD software was applied to design the self-parking framework and flat-topped mesa. These were fabricated at the same time by the anisotropic wet etching technique. The microball lens array was batch-fabricated with the microelectromechanical systems technique and batch-assembled onto the coupling platform. The design of the optical platform is able to control the distance between the fiber, the microball lens and the vertical mirror. Therefore, it can enhance the coupling efficiency. Furthermore, not only does it provide an accurate coupling distance, but also it reduces the cost of the micro-assemblage.

3D Thermoelectric Structures Derived from a New Mixed Micromachining Process

This paper proposes an innovative 3D thermoelectric structure which significantly reduce the componet size without deterioration of sensor performance. Based on complementary metal-oxide-semiconductor (CMOS) transistor compatible process, this 3D thermoelectric structure is demonstrated and fabricated by combining front-side silicon anisotropic wet etching and aluminum sacrificial layer etching technique. The voltage responsivity of derived 3D thermoelectric structure with 180×180 µm2 pixel size can be as high as 190 V/W in vacuum. This new thermoelectric structure shows its potential to be an excellent pixel structure of infrared sensor array for infrared recognition applications.

Designing, simulation and realization of in-plane operating micro valves, using new etching techniques

Design, simulation, fabrication and measurement results of a new method to fabricate in-plane oriented micro valves with use of an-isotropic wet chemical etching techniques are reported. The method is very engaging due to the simplicity, low demands on cleanroom resources, high accurate controllability and wafer-thickness independence. Integration in micro systems is facilitated by the unique possibility to obtain in-plane working devices. Performed analytical and numerical simulations as well as measurements of a duckbill valve demonstrate the functionality.

Fabrication of silicon field emission points for vacuum microelectronics by wet chemical etching

The fabrication of sharp silicon tips for field emission cathodes has been investigated using anisotropic and isotropic wet chemical etching techniques. Formulations of potassium hydroxide, water and alcohol are used as the anisotropic etchants. The effects of isopropyl, secondary butyl and tertiary butyl alcohols on tip formation are examined. An isotropic etchant using a mixture of hydrofluoric, nitro and acetic acids is also used to form similar cathode structures for comparison. The silicon needles formed are intended for use in vacuum microelectronic devices.