Deepak Uttamchandani

Measurement of the mechanical properties of silicon microresonators

Abstract A novel technique for the simultaneous determination of the strain and Youngs modulus of a silicon microresonator is reported. The lowest two symmetric vibration modes of a single resonator are excited and their frequencies measured. The measured frequencies are compared with a theoretical model. The strain is determined by substituting the ratio of the two frequencies into the model. The calculated strain is then substituted into a characteristic equation to yield Youngs modulus. The measured value for Youngs modulus is 1.31×1011 Pa, which is close to that of pure silicon, 1.30×1011 Pa.

Measurement of Young's modulus and internal stress in silicon microresonators using a resonant frequency technique

The values of Youngs modulus and internal stress in boron doped silicon microresonators fabricated by anisotropic etching techniques are reported. An array of resonators has been fabricated on a (100) orientation substrate and their resonant frequencies measured. Using the measured data, and equations relating the resonant frequencies to mechanical properties, the Youngs modulus of the boron doped silicon is calculated to be 1.33*1011 Pa whilst the built-in stress is calculated to be 1.12*108 Pa.

Scalable electrothermal MEMS actuator for optical fibre alignment

A new geometry of high-force electrothermal actuator is demonstrated using microelectromechanical systems technology. The actuator consists of two sets of inclined, parallel, suspended beams, which are tethered at one end and linked together at the other. The first set is divided into two halves, which are connected in series and heated electrically. The second set acts as a tether for the first, so that differential thermal expansion gives rise to a lateral deflection. The design can be scaled easily to increase the actuation force, which is sufficient to deflect a cantilevered optical fibre. A bi-directional fibre alignment device is formed from two opposed actuators, which are designed to grip the fibre, and a set of fixed mounting features. Prototype devices are demonstrated by deep reactive ion etching of bonded silicon-on-insulator, and in-plane alignment of single-mode fibre is demonstrated.

Phase shifted Bragg gratings formed in optical fibres by post-fabrication thermal processing

Fibre Bragg gratings have been post-fabrication processed using localised heat treatment, with significant changes to their transmission and reflection characteristics being observed. Experimental results of the spectral changes, together with an explanation of their origin, are provided in this article.

Modified J 1 … J 4 method for linear readout of dynamic phase changes in a fiber-optic homodyne interferometer

Fiber-optic interferometers have been studied extensively for sensing applications. Recently a technique described as the J(1) ... J(4) technique was reported for the linear measurement of dynamic phase changes in a fiber interferometer that requires no phase bias and for which the measurement is independent of random phase fluctuations. However, the implementation of the J(1) ... J(4) technique is limited because only the magnitude of the J(1) ... J(4) Bessel components can be measured on a spectrum analyzer without information available on the sign of the Bessel function. Here a modified signal-processing technique that overcomes the limitations mentioned above is described.

Infrared detection of transformer insulation degradation due to accelerated thermal aging

Regular monitoring of the paper insulation of electrical windings is necessary to ensure safe and reliable operation of oil-paper insulated electrical transformers. The degradation of the paper insulation due to thermal aging yields furanic derivatives which are specific to the paper and cannot be produced by general oxidation of the oil. The concentration of such furan compounds in the oil gives an accurate indication of the condition of the paper insulation. Normally, off-line methods such as HPLC (high performance liquid chromatography) are applied to periodically assess the furan concentration within oil samples which have been extracted from the transformer. We report experimental findings on the production of the furan compound FFA (furfuraldehyde) in an oil-paper system subject to accelerated thermal aging. Our approach is based on IR spectroscopy. This technique could lay the basis for the construction of direct online monitoring equipment suitable for monitoring of transformer winding insulation.

Study of scratch drive actuator force characteristics

Microactuators are one of the key components in MEMS technology, and various designs have been realized through different fabrication processes. One type of microactuator commonly used is the scratch drive actuator (SDA) that is frequently fabricated by surface micromachining processes. An experimental investigation has been conducted on the force characteristics of SDAs fabricated using the JDSU Microsystems MUMPs process. One-, two-, three- and four-plate SDAs connected to box-springs have been designed and fabricated for these experiments using MUMPs run 44. The spring constant for the box-springs has been calculated by FEM using ANSYS software. The product of the spring constant and spring extension is used to measure the forces produced by these SDAs. It is estimated that the forces produced exceed 250 μN from a one-plate SDA and 850 μN from a four-plate SDA.

Measurement of the Anisotropy of Young's Modulus in Single-Crystal Silicon

In (100) silicon wafers, the most commonly used in microelectromechanical systems (MEMS) fabrication, the value of Youngs modulus of a MEMS structure can vary by over 20%, depending on the structures orientation on the wafer surface. This anisotropy originates from the crystal structure of silicon. We have directly measured the anisotropy of Youngs modulus in the (100) plane of silicon from the measured resonance frequencies of a “wagon-wheel” test structure comprising an arc of identical microcantilevers fabricated in the structural layer of a (100) silicon-on-insulator wafer. The direction of the principal axis of the cantilevers increased from 0° to 180 ° in 10° steps with respect to the [110] direction, allowing the angular dependence of Youngs modulus to be experimentally mapped out. The Youngs modulus was measured to have a value of 170 GPa ± 3 GPa at 0° and 90 ° to the [110] direction and a value of 131 GPa ± 3 GPa at ±40° and ±50° to the [110] direction. The measured values of Youngs modulus and their angular dependence agree very well with the theoretical values that were recently reported, thereby experimentally verifying the theoretical calculations.

Integrated self-assembling and holding technique applied to a 3-D MEMS variable optical attenuator

The application of polysilicon/gold bimorph stress-induced curved beams for three-dimensional self-assembly of MEMS devices is reported. The mechanical principle behind this self-assembling procedure is presented and comparison with current assembling methods are made. With this self-assembling technique, no postprocessing is required. A free-space optical MEMS device in the form of a variable optical attenuator (VOA) has been fabricated and self-assembled using this technique. The angular elevation of the self-assembled structures and the attenuation characteristics of the optical MEMS device are reported. The VOA has a measured dynamic attenuation range of 44 dB at 1.55 /spl mu/m optical wavelength. The bending of the bimorph beams is also temperature controllable, and the thermal behavior of the beams is also reported.

Modal propagation within ARROW waveguides

Abstract The standard transfer matrix method is applied to the antiresonant reflecting optical waveguides in SiO 2 -Si structures. The results provide the first accurate picture of dispersion and attenuation of several TE-type ARROW modes at the wavelength of 1.3 μm.