Research on the processing, structure, properties and reliability of metal films and metallic microdevice elements is reviewed. Recent research has demonstrated that inelastic deformation mechanisms of metallic films and microelements are a function of temperature, encapsulation, and dimension. Reduced dimension can lead to strengthening or softening, depending on the temperature and strain rate. These results will help in the analysis and prediction of the stress state of films and microelements as a function of their thermal history. Experimental characterization and modeling of stress evolution during film formation has also been undertaken. New microelectromechanical devices have been developed for in situ measurements of stress during processing, and experiments relating stress and structure evolution are underway for electrodeposition and reactive film formation as well as vapor deposition. Experiments relating current-induced stress evolution (electromigration) to the reliability of Cu based interconnects are also being carried out. / Singapore-MIT Alliance (SMA)

In this thesis, a new model is formulated for a piezoelectric membrane and fluid motion in a microchannel heat engine. A new slug flow model is developed for droplet motion in a circular cross-section channel. The model includes friction, pressure, viscous and thermocapillary forces on the droplet. This thesis examines the concept of a piezoelectric device at one end of the channel to generate electricity from thermocapillary pumping of the droplet within the microchannel. The slug flow model is used to predict the flow energy needed to convert the thermocapillary pumping into electrical energy. A thin membrane design of a piezoelectric device is developed and modelled with the slug flow approximation. The deformation of the piezoelectric membrane is analyzed. The deformation is found to be a function of the air pressure in the closed microchannel and the displacement of the droplet along the microchannel. This was formulated based on the bending of a thin plate (representing the membrane). The displacement relates to the final output voltage of the design. The direct piezoelectric effect was also examined to determine a relationship between the output voltage and induced stress on the membrane by the force of air. Results are presented for a micro heat engine configuration containing a single membrane on one side of the droplet. It was found that the deformation of the membrane and the output voltage were directly proportional to the displacement of the droplet. A relatively small output voltage was gained from a complete cycle of the droplet. A sensitivity study was performed by varying the channel dimensions along with the dimensions of the piezoelectric membrane. The coupling factor of the piezoelectric membrane was varied to examine its effect on the output voltage. It was found that a larger channel and thinner membrane resulted in a larger output voltage. Materials with a large piezoelectric constant were found to have the largest output voltage, as opposed to those with a lower dielectric constant. / UOIT

Advances in the synthesis of micrometer and nanometer-sized materials have resulted in a range of novel materials having unique properties. Characterizing those materials is important for understanding their properties and exploring their applications. Physically manipulating those materials is important for constructing devices. This thesis develops tools and techniques for the manipulation and characterization of micro and nanomaterials. A microelectromechanical systems (MEMS) microgripper is developed to pick and place micro-objects, achieving high repeatability, accuracy, and speed. The adhesion forces at the microscale are overcome by actively releasing the adhered micro-object from the microgripper. A microrobotic system is built based on this microgripper and realizes automated pick-and-place of microspheres to form patterns. To characterize the electrical properties of one-dimensional nanomaterials, a nanorobotic system is developed to control four nanomanipulators for automated four-point probe measurement of individual nanowires inside a scanning electron microscope (SEM). SEM is used as a vision sensor to realize visual servo control and contact detection. To characterize the electromechanical properties of individual nanowires, a MEMS device is designed and fabricated that is capable of simultaneous tensile testing and current-voltage measurement of a nanowire specimen. A nanomanipulation procedure is developed to transfer a single nanowire from its growth substrate to the MEMS device in SEM. The piezoresistive properties of silicon nanowires are characterized. A nanomanipulation system is developed that is capable of being mounted onto and demounted from the SEM specimen stage without opening the high-vacuum chamber. The system architecture allows the nanomanipulators to be transferred through the SEM load-lock. This advance facilitates the replacement of end-effectors and circumvents chamber contamination due to venting.

A prototype acoustic streaming pump for microfluidic applications was developed. A novel integration scheme was devised based on the acoustic reflector concept. Numerical simulations were conducted to predict the flow patterns around the transducer. Ultrasound transducers using P(VDF-TrFE) as the piezoelectric element were fabricated using lithography-based microfabrication technology. Silicon channels were fabricated using anisotropic etching. A heat-press bonding technique was adopted to bond the transducers with the silicon chips using CYTOP fluoropolymer as the adhesive. The piezoelectric transducers were characterized to have a resonance frequency of 82 MHz. Micro-PIV experiments were performed in the near and far-fields of the ultrasonic transducer/pump. The near field experiments showed complex flow patterns that could enhance mixing. Estimates of the pumping pressure were obtained using transient flow velocities in the far-field. Conservative estimates indicate the total back pressure the micropump can pump against is 39 Pa. Future research directions were suggested.

A prototype acoustic streaming pump for microfluidic applications was developed. A novel integration scheme was devised based on the acoustic reflector concept. Numerical simulations were conducted to predict the flow patterns around the transducer. Ultrasound transducers using P(VDF-TrFE) as the piezoelectric element were fabricated using lithography-based microfabrication technology. Silicon channels were fabricated using anisotropic etching. A heat-press bonding technique was adopted to bond the transducers with the silicon chips using CYTOP fluoropolymer as the adhesive. The piezoelectric transducers were characterized to have a resonance frequency of 82 MHz. Micro-PIV experiments were performed in the near and far-fields of the ultrasonic transducer/pump. The near field experiments showed complex flow patterns that could enhance mixing. Estimates of the pumping pressure were obtained using transient flow velocities in the far-field. Conservative estimates indicate the total back pressure the micropump can pump against is 39 Pa. Future research directions were suggested.

Advances in the synthesis of micrometer and nanometer-sized materials have resulted in a range of novel materials having unique properties. Characterizing those materials is important for understanding their properties and exploring their applications. Physically manipulating those materials is important for constructing devices. This thesis develops tools and techniques for the manipulation and characterization of micro and nanomaterials. A microelectromechanical systems (MEMS) microgripper is developed to pick and place micro-objects, achieving high repeatability, accuracy, and speed. The adhesion forces at the microscale are overcome by actively releasing the adhered micro-object from the microgripper. A microrobotic system is built based on this microgripper and realizes automated pick-and-place of microspheres to form patterns. To characterize the electrical properties of one-dimensional nanomaterials, a nanorobotic system is developed to control four nanomanipulators for automated four-point probe measurement of individual nanowires inside a scanning electron microscope (SEM). SEM is used as a vision sensor to realize visual servo control and contact detection. To characterize the electromechanical properties of individual nanowires, a MEMS device is designed and fabricated that is capable of simultaneous tensile testing and current-voltage measurement of a nanowire specimen. A nanomanipulation procedure is developed to transfer a single nanowire from its growth substrate to the MEMS device in SEM. The piezoresistive properties of silicon nanowires are characterized. A nanomanipulation system is developed that is capable of being mounted onto and demounted from the SEM specimen stage without opening the high-vacuum chamber. The system architecture allows the nanomanipulators to be transferred through the SEM load-lock. This advance facilitates the replacement of end-effectors and circumvents chamber contamination due to venting.

A delay line phase shifter for the 30-70 GHz range is presented that uses an aluminum micro-ribbon array fabricated in the ground plane of a microstrip transmission line. Phase shift is achieved by changing the propagation velocity of an RF signal in the transmission line by controlling the effective permittivity of the substrate. This is done by actuating the micro-ribbons away from the substrate. This phase shifter has the benefits of analog phase shifts and high Figure of Merit. Simulations were done to model the micro-ribbon deflections, transmission line performance and phase shift. Arrays of 5, 10, and 20 μm wide micro-ribbons were fabricated and tested. At 40.80 GHz, the 20 μm wide micro-ribbons had a measured phase shift of 33º with an actuation voltage of 120 V. The corresponding Figure of Merit was a negative value indicating that there was no line loss due to ribbon deflection. / February 2008

Capacitive micromachined ultrasonic transducers (CMUTs) have proven themselves to be excellent candidates for medical ultrasonic imaging applications. The use of semiconductor fabrication techniques facilitates the fabrication of high quality arrays of uniform cells and elements, broad acoustic bandwidth, the potential to integrate the transducers with the necessary electronics, and the opportunity to exploit the benefits of batch fabrication. In this thesis, the design, fabrication and testing of one- and two-dimensional CMUT arrays using a novel wafer bonding process whereby the membrane and the insulation layer are both silicon nitride is reported. A user-grown insulating membrane layer avoids the need for expensive SOI wafers, permits optimization of the electrode size, and allows more freedom in selecting the membrane thickness, while also enjoying the benefits of wafer bonding fabrication. Using a row-column addressing scheme for an NxN two-dimensional array permits three-dimensional imaging with a large reduction in the complexity of the array when compared to a conventional 2D array with connections to all N2 elements. Only 2N connections are required and the image acquisition rate has the potential to be greatly increased. A simplification of the device at the imaging end will facilitate the integration of a three-dimensional imaging CMUT array into either an endoscope or catheter which is the ultimate purpose of this research project. To date, many sizes of transducers which operate at different frequencies have been successfully fabricated. Initial characterization in terms of resonant frequency and, transmission and reception in immersion has been performed on most of the device types. Extensive characterization has been performed with a linear 32 element array transducer and a 32x32 element row-column transducer. Two- and three-dimensional phased array imaging has been demonstrated.

¡@¡@Accompanying with the development of MEMS technology, microstages have been used for many years. Most of the studies on microstages have been aimed at the application of new actuators, materials and fabrication process in recent years. However, the systematic way for designing new microstages with the mechanism conceptual design approach still needs some more input. ¡@¡@The objective of this study is to establish a methodology to design new microstages employing the concept of mechanism design. First of all, new microstages for microassembly have been analyzed according to the basic requirements from the mechanism. Afterwards, the concept of microjoint has been presented and used in the synthesis of microstages. Besides, a flow chart of design procedure has been presented and seven kinds of microstages are achieved accordingly. Finally, the FEM simulation of the synthesized microstage illustrates the desirable results that reveal the good agreement with the expected motion. It is shown that this study can be efficiency applied to the design of micro scale devices.

The MEMS technology has been developed for many years. Micro-assembly becomes more and more important in this years. Microfasteners play a critical role in micro-assembly due to their simple configuration and easy to be fabricated. The objective of this study is to utilize the phenomenon observed, that fits the definition of the degree of freedom of general mechanisms, and to synthesize new microfasteners employing the concept of mechanism design. Firstly, microfasteners are analyzed based on the need. After synthesizing new microfasteners in micro-scale, they are transformed into compliant mechanisms in micro-scale. By establishing geometry, FEM is applied to simulate the situation of insertion and retention, and to check if bucking will happen. Finally, the retention force is improved by changing the width of links. The insertion force, retention force, and stress are considered for selecting feasible configurations. An example of microgear set mechanism is introduced to demonstrate the assembly of the microgear set after microfabrication process with large backlash.