1. Introduction and overview 2. Film stress and substrate curvature 3. Stress in anisotropic and patterned films 4. Delamination and fracture 5. Film buckling, bulging and peeling 6. Dislocation formation in epitaxial systems 7. Dislocation interactions and strain relaxation 8. Equilibrium and stability of surfaces 9. The role of stress in mass transport.

Thin Film Materials: Stress, Defect Formation and Surface Evolution

The electrostriction of elastomeric polymer dielectrics with compliant electrodes is potentially useful as a small-scale, solid-state actuator technology. Electrostrictive polymer (EP) materials are capable of efficient and fast response with high strains (> 30%), good actuation pressures (up to 1.9 MPa), and high specific energy densities (up to 0.1 J g−1). In this article, the mechanism of electrostriction is shown to be due to the electrostatic attraction of free charges on the electrodes. Although EP actuators are electrostatics based, they are shown to produce 5–20 times the effective actuation pressure of conventional air-gap electrostatics at the same electric field strength. The thin uniform dielectric films necessary for fabrication of EP actuators have been fabricated by techniques such as spin coating, casting, and dipping. A variety of materials and techniques have been used to produce the compliant electrodes, including lift-off stenciling techniques for powdered graphite, selective wetting of ionically conductive polymers, and spray coating of carbon blacks and fibrils in polymeric binders. Prototype actuators have been demonstrated in a variety of configurations such as stretched films, stacks, rolls, tubes, and unimorphs. Potential applications of the technology in areas such as microrobots, sound generators, and displays are discussed in this article.

Electrostriction of polymer dielectrics with compliant electrodes as a means of actuation

The micromachining technology that emerged in the late 1980s can provide micron-sized sensors and actuators. These micro transducers are able to be integrated with signal conditioning and processing circuitry to form micro-electromechanical-systems (MEMS) that can perform real-time distributed control. This capability opens up a new territory for flow control research. On the other hand, surface effects dominate the fluid flowing through these miniature mechanical devices because of the large surface-to-volume ratio in micron-scale configurations. We need to reexamine the surface forces in the momentum equation. Owing to their smallness, gas flows experience large Knudsen numbers, and therefore boundary conditions need to be modified. Besides being an enabling technology, MEMS also provide many challenges for fundamental flow-science research.

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Micro-electro-mechanical-systems (mems) and fluid flows

We review the methods which have been developed over the past several years to determine the behavior of solids whose properties vary randomly at the microscopic level, with principal attention to systems having composition variation on a well-defined structure (random "alloys"). We begin with a survey of the various elementary excitations and put the dynamics of electrons, phonons, magnons, and excitons into one common descriptive Hamiltonian; we then review the use of double-time thermodynamic Green's functions to determine the experimental properties of systems. Next we discuss these aspects of the problem which derive from the statistical specification of the microscopic parameters; we examine what information can and cannot be obtained from averaged Green's functions. The central portion of the review concerns methods for calculating the averaged Green's function to successively better approximation, including various self-consistent methods, and higher-order cluster effects. The last part of the review presents a comparison of theory with the experimental results of a variety of properties---optical, electronic, magnetic, and neutron scattering. An epilogue calls attention to the similarity between these problems and those of other fields where random material heterogeneity has played an essential role.

The theory and properties of randomly disordered crystals and related physical systems

A Three Dimensional Structure (3DS) Memory (100) allows for physical separation of the memory circuits (103) and the control logic circuit (101) onto different layers (103) such that each layer may be separately optimized. One control logic circuit (101) suffices for several memory circuits (103), reducing cost. Fabrication of 3DS memory (100) involves thinning of the memory circuit (103) to less than 50 microns in thickness and bonding the circuit to a circuit stack while still in wafer substrate form. Fine-grain high density inter-layer vertical bus connections (105) are used. The 3DS memory (100) manufacturing method enables several performance and physical size efficiencies, and is implemented with established semiconductor processing techniques.

Three dimensional structure memory

A method of redirecting light using an actuatable two-layer diffraction grating structure (50), the method having applications in wavelength-division multiplexed systems. The grating structure having a plurality of actuatable grating elements (52).

Methods and apparatus for diffractive optical processing using an actuatable structure

The use of polyimide (PI) in integrated circuits either as a passivant or as an interlevel dielectric requires an understanding of the potential for transfer of contaminant ions, always present to some degree in device-grade PI, from the PI to other device constituents. Sodium, in particular, if transferred from PI to SiO2 where it is relatively mobile at typical device operating temperatures, could affect device thresholds and create a reliability problem. In this paper, the quasistatic Q-V technique of Brown using metal-PI-SiO2-Si structures has been applied to the quantitative study of the transfer of Na between PI and SiO2. Removal of the PI after cure or after application of bias-temperature stress has been used to demonstrate that (1) quantitative, reversible ion transfer between PI and SiO2 does occur at temperatures above 200°C in the presence of an applied bias, but (2) in the absence of an applied bias, Na ions are not transferred from PI to SiO2 during PI cure at 350°C. It is also shown that the kinetics of Na transfer from PI to SiO2 in the presence of a bias are dominated by an activated diffusion process, with an activation energy on the order of 2.0eV and a prefactor on the order of 2x109 cm2/s.

Sodium transport in polyimide-SiO2 systems

A thermally isolated microstructure for use in metal-oxide gas sensing applications was fabricated and tested. Using the techniques of bulk micromachining, a thin silicon membrane 5 mu m thick was fabricated and then used as a structural support during subsequent device processing. The mechanical stability of the thin silicon membrane was found to be dependent on the compressive surface-oxide thickness which induced membrane buckling. A study of the buckling criteria was examined in detail by performing etch-back experiments on a series of sequentially sized membranes and observing the transition for buckling. A linear relationship between oxide thickness and membrane edge length squared was found. The device is fabricated over the membrane on the wafer surface and consists of a sandwich of LPCVD Si/sub 3/N/sub 4/, LPCVD poly-Si and LPCVD Si/sub 3/N/sub 4/. After device fabrication, the support membranes is etched away leaving the device completely isolated from the substrate. The measured values of power consumption and thermal time constant are compared with a simple model. >

A thermally isolated microstructure suitable for gas sensing applications

: Integrated circuit technology has been used to develop a miniature dielectric cure monitor probe that combines small size with built in amplification to achieve good sensitivity down to 1 Hz, making the probe more sensitive to physical property changes than conventional dielectrometers operating at 1000 Hz. This paper describes the design and operation of the microdielectrometer chip, and the model used to determine the complex dielectric constant of the material under study. Two typical applications are illustrated by experiments. First, results of a postcure study of a Versamide 140, Epon 828 mixture are presented and compared to the results of a similar study using a conventional parallel plate capacitor. In a second experiment, several probes were placed in a 100 ml mold and used to monitor the cure of a sample of the same resin system. The data show the nonuniformity of cure within the sample, and can be explained on the basis of gelation and the temperature dependence of the dielectric properties as determined in the post-cure experiment. (Author)

Microdielectrometry: A New Method for In Situ Cure Monitoring.

Transport measurements have been performed on the conducting state of a memory-type chalcogenide glass, of composition Te81Ge15As4. DC resistivity was measured from 4°K to 300°K and indicates no carrier freeze-out occurs down to 4°K. The resistance ratio, ϱ(300°K)/ϱ(4°K), was found to be 2.5. AC conductivity measurements at room temperature showed only an 18% increase in σ(ω) up to 150 khz. Hall effect experiments at 100 Hz show no dependence of carrier concentration on temperature from 77°K to 300°K, and indicate a room temperature mobility of 85 cm2/V-sec. The sign of the Hall constant implies that the carriers are holes. Resistance was measured as a function of magnetic field from 0 to 140 kOe, at 1.6°K. The magnetoresistance was positive and proportional to H2 at low fields, with saturation beginning to set in above about 80 kOe. The results of these studies, taken in conjunction with the X-ray and NMR data, can be used to suggest a plausible model for memory behavior in chalcogenide glasses.

Stephen D. Senturia

Papers

Methods and apparatus for diffractive optical processing using an actuatable structure

Sodium transport in polyimide-SiO2 systems

A thermally isolated microstructure suitable for gas sensing applications

Microdielectrometry: A New Method for In Situ Cure Monitoring.

Transport properties of a memory-type chalcogenide glass☆