Noel D. Samaan

A study of two-step silicon anisotropic etching for a polygon-shaped microstructure using KOH solution

Abstract This paper proposes a novel fabrication method for micromechanical structures which are defined by two planes, the (111) plane and a high-index crystal plane. The structure is obtained by a two-step etching process on a (100) silicon wafer using a 40%, 85°C KOH silicon anisotropic etch solution. The (111) plane is created during the first normal anisotropic etching process and the high-index plane is obtained from a second etching step without a silicon dioxide mask. The new plane is considered as a (310) plane, having a 18.43° angle to the (100) plane. A polygon-shaped microstructure can easily be obtained by this method and the structure has excellent reproducibility due to the anisotropic characteristics of the silicon orientation. The method has been sucessfully applied to fabricate a silicon micromould for a plug-type microvalve. The results indicate exact reproduction both in size and shape of the micromould.

Application of anisotropic conductive films for realization of interconnects in micromechanical structures

A new micromachining process, the application of an anisotropic conductive film (ACF) for micromechanical structures as well as interconnection both mechanically and electrically, is reported. The film acts as a spacer and adhesive as well as an electrical conductor in the vertical direction. The process provides very flexible design scheme and simple fabrication process. New micropump structure was proposed, and simple microstructures have been fabricated and tested successfully. The full details of experiment are reported, experiments where ACF type CP 7621 (Sony Chemical Co) was used to bond p type (100) silicon wafers.

Microfabrication of capillary columns on silicon

This paper describes the design and fabrication techniques of micro capillary columns as the main components in a microengineered gas chromatography system. The system is to be developed using silicon micromachining technology, and is designed as a flexible device consisting of four basic modules: a sample injection system, an open tubular column, a gas detector system, and an electronic circuit. Being designed in a modular structure, the system can be operated in a single and multidimensional configurations. The overall device measures 6 cm X 11 cm, making it very portable for field operation. The micromachined capillary columns are isotopically etched on silicon and sealed by Pyrex glass cover plate, measuring 125 cm long, and having rectangular shaped cross sections.

A Low Temperature Direct Bonding Method Using an Electron-Beam Evaporated Silicon-Oxide Interlayer

In this work, we proposed a direct bonding method using interlayers for single crystalline silicon wafers and glass wafers. Various materials were used for interlayers of thermal oxide, sputtered nitride, electron-beam(E-beam) evaporated silicon oxide and molybdenum. After hydrophilization, samples were spin dried and mated together without external forces. Three types of solutions were used for hydrophilizing the samples. Changes of average surface roughness after hydrophilization of the single crystalline silicon wafer, thermal oxide and E-beam silicon-oxide were inspected using atomic force microscope(AFM). Bonding interfaces of the bonded pairs were observed by scanning electron microscope(SEM). Voids and non-contact areas of the bonding pairs were also inspected using infrared(IR) transmission microscope. Surface energy, tensile strength measurements and breaking tests were also done.

Fabrication of a thick nickel microvalve with truncated pyramid shape

Float type micro valves can be employed in very high output pressure micropumps. They provide a very large forward to reverse flow ratio with a low leakage flow rate at high applied pressures. The valve described in this paper is a thick metal 3D structure having an excellent dimension match to the valve orifice. The valve having a thick truncated pyramid shape was successfully manufactured using an electroplating process and a silicon mould. The mould was made by anisotropic silicon etching, the truncated pyramid shape being defined by <111> crystal planes. A fine and uniform nickel structure was obtained using an agitated nickelsulphamate electrolyte, buffered with boric acid. Because of precise crystal orientations this process allows the valve to fit snugly into the valve orifice.

Computer modeling techniques applied to pneumatically driven micropumps

In this paper, an analytical approach based on the energy relationship between microcomponents has been applied to derive the characteristics of a square diaphragm silicon micropump to consider its nonlinear effects. The methodology caters for all relevant energy terms corresponding to the stiffness of the diaphragm including bending, tensile, stretch forces, the mass of the diaphragm, and of the air in the vicinity of diaphragm. The stiffness of the pump chamber and the input/output tube, the fluidic mass and the frictional losses of the input/output tube are also incorporated in the model. Equivalent electrical circuit is derived to calculate the lumped parameters using the energy expressions. The approach is applied to the pneumatically driven micropump.

Computer-aided modeling applied to microengineered pressure sensors

The development of miniaturized diaphragm structures is highly significant to the successful realization of many microengineered devices. Most industrial designs of physical sensors are now based upon detailed finite element modeling of the mechanical microstructures using software currently available for conventional mechanics. This paper investigates the effects of miniaturization on corrugated diaphragm structures through the use of advanced computer modeling and simulation techniques. By developing detailed models of the diaphragm structures using commercial finite element analysis software it is possible to investigate the effects on diaphragm performance when diaphragms are scaled from a macro level (eg. 10 mm diameter) down to a micro level (< 1 mm diameter). Case studies are presented and comparisons are made with research work published by other workers. With subsequent sensitivity analysis it is possible to explore the critical design parameters of the microengineered diaphragms, and parameterize the diaphragm such that its performance will be compensated to some degree from limitations imposed by processing parameters.

Application of a plastic diaphragm for a silicon micropump

The authors propose the use of a thin plastic film as a diaphragm for a silicon micropump. The plastic diaphragm allows large elastic deflection comprising a microsystem with corrosion resistant and low coefficient of friction. All aspects exploited through the development of a micropump with further advantages of eliminating several processing steps when compared with microdevices employing silicon as the thin vibration element. Low viscosity epoxy resigns and 100 micrometers polyethylene sticky tapes were used to overcome the relatively poor adhesion characteristics of plastics to silicon. The polyethylene sticky tape provides the weak bond onto a silicon wafer having microstructures fabricated by silicon bulk micromachining process. Type EPOFI 40200029 (Struers) low viscosity epoxy resin was used to obtain excellent sealing and high bonding strength between the silicon substrate and the plastic diaphragm. Low viscosity epoxy led to the deep penetration of the epoxy resulting in good sealing characteristics. The diaphragm and silicon micropump developed were tested with an external pneumatic actuator and showed excellent performance at pressures in the range of 0 - 30 psi.