THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

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

Surface micromachining is characterized by the fabrication of micromechanical structures from deposited thin films. Originally employed for integrated circuits, films composed of materials such as low-pressure chemical-vapor-deposition polycrystalline silicon, silicon nitride, and silicon dioxides can be sequentially deposited and selectively removed to build or "machine" three-dimensional structures whose functionality typically requires that they be freed from the planar substrate. Although the process to accomplish this fabrication dates from the 1960's, its rapid extension over the past few years and its application to batch fabrication of micromechanisms and of monolithic microelectromechanical systems (MEMS) make a thorough review of surface micromachining appropriate at this time. Four central issues of consequence to the MEMS technologist are: (i) the understanding and control of the material properties of microstructural films, such as polycrystalline silicon, (ii) the release of the microstructure, for example, by wet etching silicon dioxide sacrificial films, followed by its drying and surface passivation, (iii) the constraints defined by the combination of micromachining and integrated-circuit technologies when fabricating monolithic sensor devices, and (iv) the methods, materials, and practices used when packaging the completed device. Last, recent developments of hinged structures for postrelease assembly, high-aspect-ratio fabrication of molded parts from deposited thin films, and the advent of deep anisotropic silicon etching hold promise to extend markedly the capabilities of surface-micromachining technologies.

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Surface micromachining for microelectromechanical systems

High aspect ratio (HAR) silicon etch is reviewed, including commonly used terms, history, main applications, different technological methods, critical challenges, and main theories of the technologies. Chronologically, HAR silicon etch has been conducted using wet etch in solution, reactive ion etch (RIE) in low density plasma, single-step etch at cryogenic conditions in inductively coupled plasma (ICP) combined with RIE, time-multiplexed deep silicon etch in ICP-RIE configuration reactor, and single-step etch in high density plasma at room or near room temperature. Key specifications are HAR, high etch rate, good trench sidewall profile with smooth surface, low aspect ratio dependent etch, and low etch loading effects. Till now, time-multiplexed etch process is a popular industrial practice but the intrinsic scalloped profile of a time-multiplexed etch process, resulting from alternating between passivation and etch, poses a challenge. Previously, HAR silicon etch was an application associated primarily with microelectromechanical systems. In recent years, through-silicon-via (TSV) etch applications for three-dimensional integrated circuit stacking technology has spurred research and development of this enabling technology. This potential large scale application requires HAR etch with high and stable throughput, controllable profile and surface properties, and low costs.

High aspect ratio silicon etch: A review

Non-ideal effects in organic-inorganic materials for gas separation membranes

A review of the chemical reaction mechanism and kinetics for hydrofluoric acid etching of silicon dioxide for surface micromachining applications

Selective encapsulation of a micro electro-mechanical pressure sensor provides for protection of the wire bands ( 140 ) through encapsulation while permitting the pressure sensor diaphragm ( 121 ) to be exposed to ambient pressure without encumbrance or obstruction. Selective encapsulation is made possible by the construction of a protective dam ( 150 ) around the outer perimeter of a pressure sensor diaphragm ( 121 ) to form a wire bond cavity region between the protective dam ( 150 ) and the device housing ( 105 ). The wire bond cavity may be encapsulated with an encapsulation gel ( 160 ) or by a vent cap ( 170 ). Alternatively, the protective dam ( 150 ) may be formed by a glass frit pattern ( 152 ) bonding a cap wafer ( 151 ) to a device wafer ( 125 ) and then dicing the two-wafer combination into individual dies with protective dams attached.

Micro electro-mechanical system sensor with selective encapsulation and method therefor

A vertically integrated sensor structure (60) includes a base substrate (71) and a cap substrate (72) bonded to the base substrate (71). The base substrate (71) includes a transducer (78) for sensing an environmental condition. The cap substrate (72) includes electronic devices (92) formed on one surface to process output signals from the transducer (78). The sensor structure (60) provides an integrated structure that isolates sensitive components from harsh environments.

Vertically integrated sensor structure and method

The key process in silicon surface micromachining is the selective etching of silicon dioxide sacrificial layers with hydrofluoric acid. This paper discusses experimental sacrificial layer etching results. The etching reaction shifts from kinetic controlled to diffusion controlled as the etch channel dissolves. Test structures consist of several low pressure chemical vapor deposited (LPCVD) phosphosilicate glass (PSG) isolated etch channels having widths ranging from 2 to 50 μm underneath transparent silicon‐rich LPCVD silicon nitride or thin (1500 A) LPCVD polycrystalline silicon structural layers. Etching is monitored at timed intervals through this structural layer. Diffusion‐limitations are observed at long times. After 20 min in concentrated , etch fronts have moved 25% less than the initial etch rate would suggest. In addition, increasing the phosphorus content in PSG thin films, increasing the concentration, and the addition of to solutions increases the initial etch rate of silicon dioxide sacrificial layers. Buffered and surfactant buffered did not enhance the etching of silicon dioxide sacrificial layers. The addition of fluosilicic acid to decreased the initial etch rate of silicon dioxide but did not affect the diffusion rate of in water for low concentrations of . Etch channel width, sacrificial layer thickness, structural material choice and stress condition, and applied stress did not affect the sacrificial layer etch process rate.

Hydrofluoric Acid Etching of Silicon Dioxide Sacrificial Layers I . Experimental Observations

Etching kinetics for several silicon dioxide films in various hydrofluoric acid solutions have been studied. The low temperature silicon dioxide films were deposited at 450 o C and 300 mTorr in SiH 4 , O 2 , and PH 3 and annealed at 950 o C for 1 h. The thermal oxides were grown at 1100 o C in H 2 O and O 2 . Four hydrofluoric acid solutions were used: dilutions of 49 weight percent HF with deionized water, buffered hydrofluoric acid, surfactant-buffered hydrofluoric acid, and hydrofluoric acid/hydrochloric acid mixtures. Expressions for etch rate as a function of hydrofluoric acid concentration are presented

David J. Monk

Papers

A review of the chemical reaction mechanism and kinetics for hydrofluoric acid etching of silicon dioxide for surface micromachining applications

Micro electro-mechanical system sensor with selective encapsulation and method therefor

Vertically integrated sensor structure and method

Hydrofluoric Acid Etching of Silicon Dioxide Sacrificial Layers I . Experimental Observations

Determination of the Etching Kinetics for the Hydrofluoric Acid/Silicon Dioxide System