Robert N. Dean

Applications of Microelectromechanical Systems in Industrial Processes and Services

This paper presents a review of the current and future applications of microelectromechanical systems (MEMS) in the industrial sector. A historical perspective of the origin and development of MEMS is presented, as well as the traditional and innovative fabrication techniques. The process flow of computer-aided design and simulation is also discussed. After that, several of the most important applications of microsystems in the manufacturing and production sectors are enumerated and described. Two case examples are discussed in depth: gyroscopes for the measurement of angular movement, where the basic laws are provided, and a thorough review of existing devices is presented; and particle production devices for the generation of micrometer-sized droplets, where the two most common techniques are compared, along with the challenges that remain open. Finally, some conclusions and perspectives for the future are presented and discussed.

Evaluation and comparison of silicon and gallium nitride power transistors in LLC resonant converter

Silicon Power MOSFETs, with more than thirty years of development, are widely accepted and applied in power converters. Gallium Nitride (GaN) power devices are commercially available in recent years [1], but the device performance and application have not been fully developed. In this paper, GaN devices are compared with state-of-art Si devices to evaluate the device impact on soft-switching DC-DC converters, like LLC resonant converter. The analytical approach of device selection and comparison are conducted and loss related device parameters are derived. Total device losses are compared between Si and GaN based on these parameters. GaN shows less loss compared with Si, yielding approximately a 20% reduction of total device loss. Two 300 W, 500 kHz, 48 V-12 V GaN-based and Si-based converter prototypes are built and tested. Since the body diode forward voltage drop of GaN device is high, the dead time is adjusted to minimize the body diode conduction period. The peak efficiency of the GaN-based converter is 97.5%, and the full load efficiency is 96.1%, which is around 0.3% higher than the Si-based converter at full load. The test results shows that, although GaN device has lower loss, the improvement of converter efficiency is not much. The reason is that the transformer loss accounts for more than 60% of total loss. Therefore, a transformer which fits the GaN device characteristic need to be further investigated.

A Characterization of the Performance of a MEMS Gyroscope in Acoustically Harsh Environments

Microelectromechanical systems (MEMS) gyroscopes are typically smaller and less expensive than their macroscale counterparts. For this reason, they are being used in many new applications, including in harsh environments. It has been well documented that the performance of unprotected MEMS gyroscopes can be deleteriously affected by exposure to mechanical shock or high-frequency vibrations. The results of this investigation experimentally demonstrate that MEMS gyroscopes are also susceptible to high-power high-frequency acoustic noise when acoustic energy frequency components are close to the resonating frequency of the gyroscopes proof mass. Additionally, due to microfabrication tolerances and the resulting differences between otherwise identical devices, there can be significant differences in the acoustically sensitive bandwidth between otherwise identical MEMS gyroscopes. This phenomenon is characterized for the ADXRS300 MEMS gyroscope.

A Capacitive Fringing Field Sensor Design for Moisture Measurement Based on Printed Circuit Board Technology

Interdigitated electrode capacitive fringing field sensors have been utilized in numerous applications. Although various technologies are used to realize these types of sensors, printed circuit board technology is particularly advantageous for realizing this type of sensor through fabricating the interdigitated electrode structures in the patterned Cu foil. Additionally, the solder mask coating can insulate the electrodes to prevent shorting in the presence of water. Using this approach, prototype sensors were designed, simulated, fabricated, and successfully evaluated. Applications include water detection and quantity measurement and soil moisture content measurement.

Ultra-thin, flexible electronics

Ultra-thin, flexible electronics are advantageous for integration into biomedical sensors, wearable electronics, multifunction surfaces and low profile applications. Although flexible interconnects have been successfully demonstrated for these applications [1], the embedding of thinned, flexible semiconductor die will greatly enhance the application of this technology. Die thinning, thin multilayer substrates and the elimination of solder joints are required to meet the thickness targets for these applications. A process sequence has been developed to achieve final thicknesses of 35–75µm.

A Digital Frequency-Locked Loop System for Capacitance Measurement

Similar to phase-locked loops, frequency-locked loops (FLLs) are useful in many applications involving waveform synchronization or synthesis. Simple logic circuit-based relaxation oscillators convert capacitance to frequency, which is a characteristic inverse relationship between output frequency and input capacitance. The oscillators logic level square-wave output can be fed into an all-digital FLL that will frequency lock to the input signal and produce a digital output word N, where N is inversely proportional to the input frequency. The result is that N is linearly proportional to the unknown capacitance in the oscillator. This novel approach allows a simple FFL implementation for capacitance measurement and is demonstrated in hardware using a capacitive sensor that measures the mass of small quantities of water with an output capacitance range of 75-185 pF.

Micromachined Vibration Isolation Filters to Enhance Packaging for Mechanically Harsh Environments

Some harsh environments, such as those encountered by missiles, rockets and various types of industrial machinery, contain high frequency mechanical vibrations. Unfortunately, some very useful components are sensitive to these high frequency vibrations. Examples include MEMS gyroscopes, oscillators and some micro-optics. Exposure to high frequency mechanical vibrations present in the operating environment can result in problems ranging from an increased noise floor to component failure. Passive micromachined silicon lowpass filter structures (spring-mass-damper) have been demonstrated in recent years. Since they usually possess a low vertical profile, they can be utilized as the packaging substrate for the sensitive component requiring vibration isolation. The performance of these filter structures is typically limited by low damping and a lack of tunability after fabrication. However, filter performance can be enhanced by integrating fluidic damping techniques with the passive filter or by integrating a ...

Bi-directional Gap Closing MEMS Actuator Using Timing and Control Techniques

We analyze a micro-electro mechanical system (MEMS) device known as a gap closing actuator (GCA) and propose two timing and control algorithms that enable bi-directional motion control. The electrostatic and mechanical force equations are defined and a model created that simulates a GCA. Two timing and control techniques are used to enable bi-directional operation without using additional mechanical or electrical actuators, but with feedback control

On the Degradation of MEMS Gyroscope Performance in the Presence of High Power Acoustic Noise

Due to their reduced size, cost, and power requirements relative to traditional gyroscopes, MEMS gyroscopic sensors are finding increasing use in many applications. It is well known that unshielded MEMS gyroscopes can be vulnerable to both mechanical shock and high frequency vibrations. The results of this investigation indicate that MEMS gyroscopes are also susceptible to high power, high frequency content acoustic noise. Acoustic energy frequency components that are close to the resonating frequency of the proof mass in the MEMS gyroscope can produce undesirable motion of the proof mass, resulting in corruption in the angular rate measurement. If the acoustic signals possess enough power in the vicinity of the sensor resonating frequency, the resulting degradation in sensor performance can be severe enough to render the angular rate measurements useless.

Impact of planar transformer winding capacitance on Si-based and GaN-based LLC resonant converter

Transformer loss, comprised of core loss and winding loss, is a critical part in the LLC resonant converter loss. Different winding structures lead to different winding losses and winding capacitances. High winding capacitance will impact the design of the LLC resonant converter. The reason is that high winding capacitance means high winding charge, which must be moved during the dead time to realize the device zero voltage turn-on. As a result, the dead time and magnetizing current will be changed, and the converter loss will be changed as well. This paper first discusses the transformer loss including core loss and winding loss. Then, four different winding structures are analyzed based on a selected core, which show the decrease of AC resistance and the increase of winding capacitance. After that, the winding capacitance model is discussed generally. Finally, the impact of winding capacitance on the design and performance of LLC resonant converter is studied. Two 48 V-12 V, 300 W Si-based and GaN-based LLC resonant converters are designed as platforms to evaluate the impact of winding capacitance. The results indicate that the GaN-based converter is well suited to the transformer with lowest winding loss but highest winding capacitance, since the GaN devices output capacitance is much lower than that of the Si device.