From MEMS to nanomachine

Urodynamic analysis is the predominant method for evaluating dysfunctions in the lower urinary tract. The exam measures the pressure during the filling and voiding process of the bladder and is mainly interested in the contraction of the bladder muscles. The data arising out of these pressure measurements enables the urologist to arrive at a precise diagnosis and prescribe an adequate treatment. A technique based on two optical fiber pressure and temperature sensors with a resolution of better than 0.1 cm H₂O (∼10 Pa), a stability better than 1 cm H₂O/hour, and a diameter of 0.2 mm in a miniature catheter with a diameter of only 5 Fr (1.67 mm), was used. This technique was tested in vivo on four patients with a real-time urodynamic measurement system. The optical system presented showed a very good correlation to two commercially available medical reference sensors. Furthermore, the optical urodynamic system demonstrated a higher dynamic and better sensitivity to detect small obstructions than both pre-existing medical systems currently in use in the urodynamic field.

A miniature high temperature, high frequency, fiber optic pressure sensor capable of operation above 1000K and frequencies above 1MHz has been developed and tested. The sensor accuracy, pressure resolution, temporal resolution and high temperature capability were first demonstrated through a series of laboratory experiments. The sensors were then tested on the forebody and inside the combustor of a full-scale X-51 configuration at fully duplicated flight conditions in the LENS II reflected shock tunnel at the CUBRC facility in Buffalo, NY. The pressure sensors displayed good run-torun repeatability and durability during the 10 run test program. Forebody and tar combustor pressure measurements respectively displayed a ω -0.8 and ω -1 decay in the power spectrum for frequencies related to fluctuations within the log layer. At low frequency, the spectra were essentially flat. In the combustor, a significant increase in the power-law decay was observed for combusting runs. On the forebody, good spectral agreement was obtained at moderate frequencies between the fiber optic and Kulite piezoresistive pressure sensors. This sensing technology enables improved measurement capabilities during ground testing where high frequency pressure measurements in high temperature high speed flows are required.

Summary form only given. MEMS (micro electro mechanical systems) and NEMS (nano electro mechanical systems ) have been developed based on silicon micromachining for practical applications. Sophisticated MEMS device used as a two-axis rotating gyroscope for navigation control system was developed. A silicon ring rotor is electrostatically levitated and rotated at 12,000rpm. The 4mm diameter ring rotor and 5m radial gap between rotor and electrode were fabricated using deep RIE (reactive ion etching) and the rotor is sandwiched between two glasses which have control electrodes. The levitation is actively controlled by force balancing in all directions using a capacitive displacement sensing and an electrostatic actuation. The rotation is based on the principle of a variable capacitance motor. The function as the high performance gyroscope and accelerometer were successfully demonstrated. Small size relays for high frequency operation are required for LSI tester. MEMS relay which uses a thermal bimetal actuator for making contact to multi-springs was developed. The springs have electrical connections to the backside using electrical feedthrough in a glass, which results in high frequency response up to 20 GHz. Excellent reliability more than 10/sup 7/ cycles was achieved owing to the hermetic scaling performed by wafer level packaging using anodic bonding of glass and silicon. Multiprobe data storage has been developed. High density electrical feedthrough in a glass was used for the interconnection to its control IC. Electrical rewritable recording on a conductive polymer film and a ferroelectric recording were performed. Electron field emitter array for the purpose of multi-column electron beam lithography was developed using carbon nano tube emitter and electrostatic lens for focusing. It was evident that hydrogen covered carbon nano tube reduces the work function for field emission and the emission noise. Highly sensitive sensors using micro-nano structures such as thin cantilevers have been developed. Bow-tie antenna for near field optical microscope and magnetic resonant force microscope will be presented.

High sensitivity fiber optic pressure sensor is in great demand in in all aspects due to its advantages. However, the current high sensitivity optical fiber pressure sensor has the problems of large size and high cost. An optical fiber pressure sensor based on all-silica Fabry-Perot interference has been proposed in this paper. The sensor consists of single mode fiber, silica capillary and diaphragm made of coreless optical fiber. The diameter of the sensor is only 125 μm. With precise control of diaphragm thinning, the diaphragm thickness of F-P sensor is only 1.477 μm, the sensor manufactured in this way has sensitivity with 12.586 rad/MPa. The sensor is ease of manufacturing and low cost. Static calibration shown the advantages of the sensor are high sensitivity, good linearity, repeatability, reliability and low hysteresis.

This paper presents an optical fibre pressure and temperature sensor (OFPTS) system, which is adapted for use as a urodynamic pressure measurement system (UPS) for differential pressure measurement with temperature compensation. The OFTPS is based on a Fabry Perot interferometer (FPI), which acts as a pressure sensor and includes an embedded fibre Bragg grating (FBG) for temperature measurement. The sensor system is evaluated in a lower urinary tract (LUT) simulator, which simulates the bladder, rectum and detrusor muscle. The system was benchmarked against a commercially available urodynamic system, at the University Hospital Limerick (UHL) Urology Clinic. Both systems demonstrate a high correlation with a relative pressure variation of less than ±2.8cmH₂O for abdominal and ±4cmH₂O for vesical pressure. The repetitive measurement of the OFPTS system in the LUT simulator against the commercial system demonstrated the high repeatability. Furthermore, the low fabrication cost makes the OFPTS a potentially interesting instrument for urodynamic and other medical applications.

In this paper, we report monolithic integration of MEMS (micro electro mechanical systems) actuators and high-voltage driver circuits into a silicon chip. Driver circuits of up to 40 V were prepared on an 8-/spl mu/m-thick SOI (silicon-on-insulator) wafer by the DMOS (double-diffused metal oxide semiconductor) processes, after which MEMS electrostatic actuators were integrated into an identical SOI layer by post-processing using DRIE (deep reactive ion etching). This technique opens up a new way of high-voltage ASIC (application specific integrated circuit) for MEMS designer. As a prototype application model, we have developed microlens optical scanners and other elementary MEMS electrostatic actuators with multi-channel driver circuits.

Optical fibre pressure sensors have potential performance advantages over electrical sensors in measuring rapid transients such as shock waves from explosive blasts. We report the development of micromachined optical fibre Fabry–Pérot pressure sensors using a silicon dioxide or nitride diaphragm and detail the fabrication stages of the sensor body and diaphragm. The planar technology used is based on silicon deep etching and direct fusion bonding of silicon wafers. Test results for both types of diaphragm are presented. Sensors with rise times better than 3 µs, range 0.1 to 1 MPa and resolution ∼500 Pa have been demonstrated in explosives trials. Despite the difference in the sign of stress for the two diaphragm types, both demonstrated excellent high-speed response to explosively generated air shocks.

A non-sequential pulsed-mode deep reactive ion etching of silicon is reported that employs continuous etching and passivation based on SF6 and H2 gases. The passivation layer, as an important step for deep vertical etching of silicon, is feasible by hydrogen pulses in proper time-slots. By adjusting the etching parameters such as plasma power, H2 and SF6 flows and hydrogen pulse timing, the process can be controlled for minimum underetch and high etch-rate at the same time. High-aspect-ratio features can be realized with low-density plasma power and by controlling the reaction chemistry. The so-called reactive ion etching lag has been minimized by operating the reactor at higher pressures. X-ray photoelectron spectroscopy and scanning electron microscopy have been used to study the formation of the passivation layer and the passivation mechanism.

Anisotropic reactive ion etching of silicon has been widely used in fabrication of diffractive optical elements, waveguides and structures of Micro-Electro-Mechanical Systems (MEMS) in recent years. It is important to achieve minimal roughness on both horizontal surfaces and sidewalls in reactive ion etching (RIE) of silicon. Now reactive ion etching of silicon in an RF parallel plate system, using SF 6 /O 2 /CHF 3 plasmas, has been experimentally studied. Black silicon method (BSM) is a powerful tool that can be used to find the best conditions under which the anisotropic etching of silicon is optimized. In the process of etching silicon, SF 6 serves as the major reactive etching species on silicon, while O 2 is added to build the passivation layer on the sidewalls and surfaces to get anisotropic profiles and CHF 3 to suppress the formation of passivation on horizontal surfaces in order to achieve smooth etch surfaces. BSM provides a convenient way to know the function of the gases adding into the RIE and to find how to adjust the proportion of the gas combination. Experimental parameters including the etching rate, selectivity, anisotropy, and self-bias voltage under different parameters have been examined through SEM and AFM. As a result, anisotropic etching conditions and the parameters corresponding to the minimal roughness on the surfaces were obtained.

In this work, a silicon-based micro-probe array was fabricated using multi-step deep reactive ion etching (DRIE) and reactive ion etching (RIE) processes. The micro-probe structure was implemented using a micromachining technique through a combination of two anisotropic DRIE and two isotropic RIE processes with a single etch mask. The cone-shaped tip height and tapered tip-end angle were experimentally varied with respect to the first DRIE depth. As the first DRIE depth was decreased, the micro-probe tip height increased and the sharpness consequently improved. The conductive layer was exposed only at the tip ends of the micro-probe to form a conical ultra-micro electrode, and it was characterised via cyclic voltammetry measurements.

We report on vertical mirrors fabricated by deep reactive ion etching of silicon. The mirror height is 75 /spl mu/m, covering the fiber core of a single-mode fiber when the latter is placed into a groove of equal depth and etched simultaneously with the mirror. To obtain a uniform etch depth, etching is stopped on a buried oxide layer. Using the buried oxide as a sacrificial layer allows to fabricate mirrors with suspension and actuation structures as well as fiber-alignment grooves in one and the same processing step. A minimal mirror thickness of 2.3 /spl mu/m was achieved, resulting in an aspect ratio higher than 30. The verticality was better than 89.3/spl deg/. In the upper part of the mirror a surface roughness below 40 nm rms was obtained. At a wavelength of 1300 nm the reflectivity of the aluminum-coated mirrors was measured to be higher than 76%. Using a reactive ion etched mirror we have fabricated an optical fiber switch with electrostatic actuation. The coupling loss in the bar state of two packaged prototypes was between 0.6 and 1.7 dB and between 1.4 and 3.4 dB in the cross state. The switching time is below 0.2 ms.

Deep reactive ion etching (DRIE) technique is a new and powerful tool in Micro-Electro-Mechanical Systems (MEMS) fabrication. A 3D DRIE simulation can help researcher understand the time-evolution of Bosch process used in DRIE. Due to the high complexity of the algorithm used in the simulation, it is necessary to develop an algorithm that can accelerate the simulation. This paper presents a parallel implementation of the 3D DRIE simulation based on GPU, built on Nvidia's Compute Unified Device Architecture (CUDA) platform. This paper also presents a fast morphological operation, which reduces the complexity of mathematical morphology operation part of the algorithm from O(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) to O(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). The experiment results show the parallel program on Nvidia GTX260+ GPU obtains about 70× to 75× speedup over the 4-threads parallel version on Intel Q6600 CPU.

The notching and stiction problem, which widely exists in silicon on insulator (SOI) microstructure fabrication, were resolved in this study. In this paper, a new plasma trench technique that is based on the deep reactive ion etching (DRIE) process is proposed. In this modified process, the deep reactive ion etching (RIE) was divided into several steps, where conformal plasma enhanced chemical vapor deposition (PECVD) oxide coating, and directional oxide etch back were employed to prevent the notching effect and the reactive ion etching (RIE) lag effect is also improved. Therefore, the microstructures regardless of the feature sizes could be realized. The stiction problem is eliminated by using dry chemical release replacing wet release in this approach, where the notching effect is used. The notching or footing effect was exploited for attaining the lateral etch following the deployment of the anisotropic plasma etching of the inductively coupled plasma (ICP). This method was proven useful for both the uniform and non-uniform feature designs. With this novel process, the high aspect ratio beams can be obtained. The thickness of the silicon layer is 75 μm, while the depth of the beams is 70 μum where the 5 μm silicon was etched to suspend the movable beams. The aspect ratio is as high as 35. Trenches with very different widths of 2.5 μm and 35 μm are also achieved at the same time.

Aspect ratio dependent etching and microloading effects are two mechanisms leading to non-uniformities in the etching of silicon using deep reactive ion etching technology. This paper focuses on the apparent presence of a critical aspect radio when etching three-dimensional MEMS structures. A mask designed to separate the effects of microloading from aspect radio dependent etching was made, and various sizes of features (3 to 1000 /spl mu/m) are etched simultaneously for different etching times (10 to 180 min) using a Bosch etching process. Experimental data exhibiting three distinct regimes for the etch rate, the corresponding critical aspect ratios, and the dependence on microloading effects are presented. Possible mechanisms governing these regimes are also postulated.

Recent process developments have permitted the highly anisotropic bulk micromachining of titanium microelectromechanical systems (MEMS). By using the metal anisotropic reactive ion etching with oxidation (MARIO) process, arbitrarily high-aspect-ratio structures with straight sidewalls and micrometre-scale features have been bulk micromachined into titanium substrates of various thicknesses, ranging from 0.5-mm sheet down to 10-microm free-standing titanium foils. Bulk micromachined structures are generally free of residual stresses and are preferred when large, rigid, flat and/or high-force actuators are desired. However, so far there has been a limited ability to select materials on the basis of specific application in bulk micromachining, primarily because of the predominance of MEMS processes dedicated to single-crystal silicon, such as silicon deep reactive ion etching. The MARIO process permits the creation of bulk titanium MEMS, which offers potential for the use of a set of material properties beyond those provided by traditional semiconductor-based MEMS. Consequently, the MARIO process enables the fabrication of novel devices that capitalize on these assets to yield enhanced functionalities that would not be possible with traditional micromechanical material systems.