Stephen M. Bobbio

Integrated force arrays

Integrated force arrays (IFAs), which are flexible metallized membranes that can be patterned using the techniques of VLSI electronics and that undergo substantial deformation when voltage is applied, have been developed. They may be configured as macroscopic actuators or used in highly articulated systems of great complexity. The theory of operation, the methods of construction, and the observational results for IFA test structures are presented.<<ETX>>

Integrated force arrays: theory and modeling of static operation

Integrated force arrays (IFAs) are a novel means of microelectromechanical actuation. They are membranes that consist of thousands of micron-scale deformable capacitors and are capable of contraction and force exertion in one dimension by application of an applied voltage. The theory and modeling of the static operation of a representative unit device and an array is presented. The electrostatic and elastic forces present in the system are considered and classical beam theory and superposition are applied to calculate the voltage-induced closure and force generation of the networks without the aid of finite element analysis. It is shown that contraction and force generation are expected at reasonable voltages for these modular structures: Ideal system contraction on the order of 40% is possible and minimum external forces of 4500 /spl mu/N/mm/sup 2/ are expected with the application of 50 V. >

High rate magnetron RIE of thick polyimide films for advanced computer packaging applications

High performance (high speed and high wiring density) computer packaging can be obtained by applying thin film technology to the multichip interconnection structure. The thickness of the layers, as determined by the electrical requirements, necessitates the use of a via-fill process in conjunction with straight-wall openings in the dielectric layers. The packaging performance and wiring density is improved through reduced via areal dimensions (increased number of lines per layer), through elimination of stepcoverage limitations, and through better planarity thus increasing the number of signal and power layers. The MCNC split cathode magnetron was found to be the best RIE system for obtaining high rate low pressure oxygen RIE of polyimide films. The polyimide etch process was studied, characterized and optimized for the anisotropic residue free etch of 4 µm to 12 µm thick polyimide films. The etched wafers were then processed through the subsequent via filling step and reproducible planar via-filling was achieved with an electroless Ni plating process.

Intracardiac ultrasound catheter using a micromachine (MEMS) actuator

Catheter based intracardiac ultrasound offers the potential for improved guidance of interventional cardiac procedures. The objective of this work is the development of catheter based, forward-looking mechanical sector scanners incorporating high frequency ultrasound transducers operating at frequencies up to 20 MHz. The current transducer assembly consists of a single 20 MHz PZT piston mounted on a polyimide table that pivots on gold plated polyimide hinges. This table-mounted transducer is tilted using a linear MEMS actuator to produce a sector scan. The prototype transducer/actuator assembly was fabricated and interfaced with a personal computer to create a single channel ultrasound scanner. This paper discusses the development of and results obtained by this real time scanning system.

Integrated force array: interface to external systems

Integrated Force Arrays (IFAs) are thin film linear actuators which operate with substantial displacement and force. The methods of attachment of these devices to external systems are under development. Our current methods to incorporate IFAs in an scanning ultrasound imaging systems as well as a new material and method for attachment will be described.

Silylated acid hardened resist process: A deep ultraviolet surface imaging technique

A deep ultraviolet surface imaging technique using a silylated acid hardened resist (SAHR) is described. The resist, Shipley XP‐8928, contains a meta, para‐cresol novolak resin which has a high optical absorbance in the deep ultraviolet (DUV). This reduces complications from substrate reflections and restricts the image to the near‐surface regions. The exposed regions, which become crosslinked, are less susceptible to vapor silylation by agents such as trimethylsilyldiethylamine (TMSDEA). The unexposed regions may be easily silylated. An anisotropic oxygen reactive ion etching is used to transfer the surface image through the bulk of the resist. This paper discusses the kinetics of silylation with TMSDEA, the resulting silicon distributions in the film before and after etch, and the lithographic performance of the process. Silicon distribution throughout the film is determined by Rutherford backscattering spectrometry and illustrated by stained cross sections. It is found that the film surface saturates a...

Silylated Acid Hardened Resist [SAHR] Technology: Positive, Dry Developable Deep UV Resists

This paper describes continuing efforts in the development of Acid Hardened Resist (AHR) systems for use in deep UV photolithography. The Silylated AHR (SAHR) process treats a highly absorbing resist, such as XP-8928, with trimethylsilyldiethylamine. The exposed, crosslinked areas show virtually no reactivity with the silylating agent, and the unexposed areas incorporate 10 to 12% by weight silicon in the film. The silicon appears to incorporate from the exterior in a constant concentration, consistent with Case II diffusion. Subsequent dry etching leads to a positive tone image. The contrast is 5, and the photospeed is ~10 mJ/cm2. Resolution of 0.5 μm line/space pairs has been demonstrated, although substantial proximity effects are encountered.

Plasma resistant modified I-line, deep UV and E-beam resists

This paper presents chemically modified photoresists for use as plasma etch masks over various substrates during patterning in IC manufacturing with sub-0.5 micron resolution. The modification consists of directly adding the modifying compounds into the photoresist solutions. The added compounds increase the Oxygen, Fluorine and Chlorine plasma resistance of photoresists, thus promoting a high etch rate selectivity with respect to other substrates and films (e.g. polyimide, PMGI, oxide, etc.).<<ETX>>

Integrated force array: positioning drive applications

Integrated Force Arrays (IFAs) are thin film membrane actuators that act as transfer devices for electrostatic force. They are capable of large amplitude motion and evidence significant energies per unit volume (eg. 8.2 erg/mm3). Devices which use IFAs as drivers to scan PZT acoustic imaging transducers are under development and will be discussed here.

Synthetic muscle actuators: applications in ultrasonic imaging and optical beam steering

There is much interest in the biomedical community in mechanically steering both high frequency ultrasound transducers and various optical beams. We are currently investigating the use of two different types of MEMS actuators, integrated force arrays (IFAs) and spiral wound transducers (SWTs). The IFA is a linear actuator that is a parallel network of hundreds of thousands of flexible capacitors that electrostatically contract, and the SWT is a patterned tape that is wound to form a circular network of flexible capacitors that can be electrostatically compressed to tilt desired structures. Using ANSYS finite element analysis, we have developed tilting polyimide support structures, which are fabricated on silicon wafers. High frequency ultrasound transducers (20-30 MHz) have been built on these structures and IFAs used to tilt them to steer the ultrasound beam in fluids. Prototype structures have produced 20 degree sector scans scanning at frequencies up to 30 Hz. IFAs have also been used along with similar support structures to steer optical laser beams up to 45 degrees at frequencies up to 60 Hz. The SWT is a more recent development that operates with much greater force than the IFA that could steer ultrasound and optical beams for similar applications.