Lorenzo Baldo

SURFACE ACOUSTIC WAVE PRESSURE SENSOR

A sensitive sensor for measurement of pressure and strain is created by fabricating a surface acoustic wave (SAW) delay line on a quartz substrate. The SAW device which acts as a band pass filter has a central frequency of 98MHz. When an external force, strain, pressure is applied to the acoustic gap, then the gap length and IDT finger spacing will change and thus cause a shift of the central frequency and of the phase. Our approach was first to generate a 98MHz signal at the input transducer and to evaluate the relative phase shift due to the pressure or the strain. The second approach was to introduce the SAW device in an oscillator loop to measure the relative variations of the central frequency. A simulation based on finite elements was carried out to compare the length variations and an experimental study of the IDTs position, substrate thickness and orientation on the sensor response.

Package design of pressure sensors for high volume consumer applications

In this abstract we outline the critical design aspects for the design of high volume pressure sensor for MEMS applications. Pressure sensor designs by their nature require the active device to be in contact with the pressure to be measured, this requirement has until now restricted the possibility of applying large volume semiconductor package manufacturing techniques to pressure sensors and hence their large scale deployment in consumer applications. The current designs of pressure sensors rely on either a separate protective membrane, a Gel-Liquid to transmit the pressure to the active device or a Gel applied on top of the sensor. The active part of the sensor is normally made up of two separate chips , the active membrane which flexes in response to external pressure the movement of which is translated into electrical signals by resistive or capacitive elements and a support chip with trapped between them a reference pressure volume. In this paper the design of a novel LGA based MEMS Pressure sensor and barometer/altimeter design are demonstrated. A single chip sensor solution is outlined with no need for the trapped reference volume between the support chip and the sensor membrane. In this single chip sensor solution the reference pressure volume is trapped within the chip itself improving both the chip dimensions and overall reliability by eliminating the joint between the two chips. The Packaging for a this single chip sensor is based on the now well established LGA sensor platform, the problem of interfacing the pressure sensor to external pressure is solved by using an exposed silicon in the over moulded package which allows the pressure sensor access to the outside pressure, reducing the overall package size for the absolute pressure sensor to 3 x 3 x 1 mm. MEMS sensor devices in general depend on their mechanical performance to translate mechanical movement into an electrical signal, the interface to the outside world, the package, is a mechanical structure that has a large influence on the device performance and must be thought of a part of the device not just as protective housing. In the case of the pressure sensor the flexible silicon membrane is influenced by the thermal stresses in the package. The design aspects that have influence on the performance of the MEMS devices are outlined, the Package and sensor devices were extensively modeled using FEA thermo-mechanical simulation with the results showing a good correlation to the final device performance. Problems encountered during the development related to device manufacturability are outlined and the solutions detailed. The final performance and reliability data is also presented demonstrating the robustness of the design solution.

Electrostatic microactuator for future hard disk drive

Hard disk drives are the most widely used data-storage medium. The TPI (track per inch) limit is related to mechanical resonances of the positioning arm and to low frequency bearing effects. A secondary actuator must be able to precisely position the R/W head, with high bandwidth, with respect to the magnetic track, without any interference with the magnetic data recorded on the disk. MEMS technology allows the fabrication of such electrostatic microactuators for the secondary stage in HDDs.

Batch fabricated silicon electrostatic micropositioner for dual stage actuation

Hard Disk Drives (HDD) are the most widely used data-storage medium. The Track Per Inch (TPI) limit is related to mechanical resonances of the positioning arm and to low frequency bearing effect. A secondary actuator must be able to position precisely with higher bandwidth the Read/Write (RW) head with respect to the magnetic track with any interference with the magnetic data recorded on the disk. MEMS technology allows the fabrication of such electrostatic microactuator for the secondary stage in the HDD. The paper presents the basics requirements for the secondary actuator for the HDD as well as the process developed to fulfill those. Accurate calculation and FEM simulation are required to lead to high performance and robust design. After the built a deep experimental analysis is ducted to confirm and refine design parameters.

Model based design optimization of micromechanical systems, based on the Cosserat theory

In this paper we present the model based design optimization on a micromechanical system which is described by a VHDL-AMS behaviour model, based on the Cosserat theory. The application is a gyroscope test structure developed by STMicroelectronics. The schematic of the microactuator is built up from component models developed in Lancaster within previous work. The equations of motion of the beam model were derived using Cosserat theory. The rigid body model was adjusted to capture the behaviour of the central disk with comb-drives of the microactuator target structure. Within the model based design optimization system MODOS developed at the University of Bremen a model optimization and a model based design optimization were performed. In this report we represent the theoretical background of the modeling and optimization process and publish the received results.

Novel process for realization of multiple-axis actuators suitable for the realization of an optical switch

This paper illustrates a novel MEMS technology that allows the creation of a multiple axis actuator / sensor trough deep silicon etching and wafer bonding techniques. As example a dual axis rotational high-stroke MEMS actuator is presented. This device can integrate a mirror to realize a device used, for example, in fully optical multiplexer. Microfabrication technology derives from our previous works and it’s based on deep silicon trench techniques as well as on wafer bonding capabilities. More over the resulting assembly after the wafer bonding is machined to proceed on realizing the complete MEMS device.