Square-extensional mode single-crystal silicon micromechanical resonator for low-phase-noise oscillator applications

A micromechanical 13.1-MHz bulk acoustic mode silicon resonator having a high quality factor (Q=130 000) and high maximum drive level (P= 0.12 mW at the hysteresis limit) is demonstrated. The prototype resonator is fabricated of single-crystal silicon by reactive ion etching of a silicon-on-insulator wafer. A demonstration oscillator based on the new resonator shows single-sideband phase noise of -138 dBc/Hz at 1 kHz offset from the carrier.     

Independent component approach to the analysis of EEG and MEG recordings

Multichannel recordings of the electromagnetic fields emerging from neural currents in the brain generate large amounts of data. Suitable feature extraction methods are, therefore, useful to facilitate the representation and interpretation of the data. Recently developed independent component analysis (ICA) has been shown to be an efficient tool for artifact identification and extraction from electroencephalographic (EEG) and magnetoencephalographic (MEG) recordings. In addition, ICA has been applied to the analysis of brain signals evoked by sensory stimuli. This paper reviews our recent results in this field.     

MROS-68K,a memory resident operating system,for MC68000

The operating system described has been designed and implemented for use in dedicated one-purpose applications, typically in real tihe. Specific attention has been paid to flexible intertask contkol. In the first installation the application system was the steering and controlling of large hydraulic devices. Typical subtasks involved were measuring, coordinate transformations, control, teaching and following robotic paths and evaluating daily material transfkrs. As a programming effort, developing the operating system was fairly reasonable being of the order of three or four months for one person, including design, coding, testing and documentation.     

Factors influencing the insulin space in cerebral cortex slices from adult and 7-day-old rats

The inulin spaces and swelling of brain cortex slices from adult and 7-day-old rats were measured under differing experimental conditions. At 37 degrees C inulin penetrated into larger compartments than at 0 degrees C in both age groups. At 37 degrees C the inulin space increased with decreasing concentration of inulin in the medium. At 0 degrees C the inulin space did not depend on the inulin concentration. The swelling of the slices at 37 degrees C diminished with increasing concentrations of inulin. Anaerobic conditions, 0.2, and 1.0 mmol/l sodium cyanide and 0.1 mmol/l dinitrophenol reduced the inulin space and caused increased swelling of the slices. 1.0 mmol/l sodium iodoacetate was ineffective. In anaerobic conditions the inulin space did not change significantly as a function of the inulin concentration. A serious disadvantage of the inulin space as an indicator of extracellular space is that its size depends on the inulin concentration used. The inulin itself may influence the size of the space to be measured. Inulin also in osmotically inactive concentrations considerably reduces the swelling of brain cortex slices.     

Spray pyrolysis deposition of zinc oxide nanostructured layers

Highly structured ZnO layers comprising well-shaped hexagonal rods were prepared by spray pyrolysis deposition of zinc chloride aqueous solutions in the temperature range of 490-560 °C. The layers were characterised by SEM, XRD and SAED. A flat ZnO film evolves into the structured layer consisting of single crystalline hexagonal elongated prisms at growth temperatures close to 500 °C and above. The rise of both the growth temperature and solution concentration increases rod dimensions. The deposition of the 0.1 mol/l solution at ∼500 °C results in crystals with a diameter of 200-300 nm and length of 800 nm. However, the rods grown at 560 °C indicate a width in the range of 400-600 nm and a length of up to 2500 nm. The deposition of the 0.05 mol/l solution at 560 °C results in the rods with a diameter of 100-300 nm and a length of 1500 nm. The increase of the concentration up to 0.2 mol/l results in branched crystals, mainly tripods with a similar leg size of 600-700 nm in width and 3000 nm in length. According to XRD, the ZnO layers grown from the 0.1 mol/l solution in the temperature range of 450-560 °C are c-axis-oriented, independent of morphology. The XRD peaks intensities ratio (I₀₀₂/I₁₀₁) of the samples deposited at 560 °C changes from 9 to 1.3 by an increase in the solution concentration from 0.05 to 0.2 mol/l and indicates that c-axis orientation vanishes at higher concentrations. We showed that ZnO nanorods with the length to diameter ratio of 30 can be prepared by spray technique using indium tin oxide-covered glass substrates instead of bare glass.     

Bonded thick film SOI with pre-etched cavities

We have studied direct bonding and thinning of pre-etched silicon wafers. Silicon-on-insulator (SOI) substrates with pre-etched cavities provide freedom to MEMS design and enable manufacturing of advanced sensor structures (sensor structures that would be difficult or impossible with conventional substrates). Cavities with different shapes and sizes were etched on to the handle wafers. The etched handle wafers were bonded to unpatterned cap wafers in air or in vacuum. The bonding quality was evaluated with scanning acoustic microscopy and with HF-etching test. After bonding, the cap wafers were thinned down with grinding and polishing. The thickness variation of silicon diaphragm over the cavities was evaluated with cross-sectional SEM. The deflection of the Si film was measured with surface profilometry. To decrease the deflection and the thickness variation of the film, different support structures were placed inside the cavities.The bonding experiments carried out with patterned wafers showed that vacuum bonding results in slightly higher bonding energy than bonding in air. With large cavity fraction (80% of total wafer area), the air bonded samples had large void on the bonded interface. With smaller cavity fractions or with vacuum bonded samples, no such voids were found. Thinning studies showed that the thickness variation of the silicon diaphragm increases with increasing cavity dimensions and with decreasing SOI layer thickness. Thickness variation can be reduced with support structures under the Si membrane.