Hirofumi Funabashi

Anisotropic etching of silicon in TMAH solutions

Abstract Detailed characteristics of tetramethyl ammonium hydroxide (TMAH, (CH3)4NOH) as silicon anisotropic etching solutions with various concentrations from 5 to 40 wt.% and temperatures from 60 to 90 °C have been studied. The etch rates of (100) and (110) crystal planes decrease with increasing concentration. The etched (100) planes are covered by pyramidal hillocks below 15 wt.%, but very smooth surfaces are obtained above 22 wt.%. Etch rates of 1.0 μ/min for the (100) plane and 1.4 μ/min for the (110) plane at 90 °C are obtained using a 22 wt.% solution. The etch-rate ratio of (111)/(100) varies from 0.02 to 0.08. The etch rate of thermally oxidized SiO2 is almost four orders of magnitude lower than that for (100) and (110) planes. The etch rates of aluminium are reduced by dissolving silicon in TMAH solution. Etch-stop techniques using a heavily boron-doped layer or p—n junction prove to be applicable to TMAH solutions.

Vibrating gyroscope consisting of three layers of polysilicon thin films

Abstract A vibrating gyroscope consisting of three layers of polysilicon thin films has been developed. It has an upper electrode over a resonating mass for detecting accurately the sensing vibration oscillated by the Coriolis force . The resonant frequencies of both the driving and sensing vibrations are controlled by the DC bias to comb electrodes that are used for detecting the driving vibration. The offset on the angular rate output due to the mechanical and electromechanical couplings is decreased by an unbalanced differential oscillation. With this tuning method and the offset reduction, the angular rate was detected. The resolution of 1° s −1 is achieved.

A Z-axis differential capacitive SOI accelerometer with vertical comb electrodes

This paper describes a differentially detecting capacitive Z-axis SOI accelerometer using a set of vertical comb electrodes. The device structure has only one silicon layer and there are no lower or upper electrodes. Z-axis acceleration was differentially detected by using a set of newly proposed vertical comb electrodes of different movable and fixed heights. The sensing area was 1.1 mm/spl times/1.1 mm/spl times/15 /spl mu/m. The performance of the accelerometer was calculated and measured experimentally to determine its linear capacitance change and voltage output against input acceleration. The measured capacitance sensitivity and its linearity were 1.1 fF/G and 0.21%, respectively.

Thermal micropressure sensor for pressure monitoring in a minute package

A thermal micropressure sensor suitable for pressure measurements in the range from 7×10−3 to 1×105 Pa has been fabricated by forming a titanium (Ti) thin-film resistor on a floating nondoped silica glass membrane, with the sensing area being as small as 60 μm×60 μm. The sensor performance is raised by: (1) increasing the ratio of gaseous thermal conduction in the total thermal conduction by sensor structure design; (2) compensating the effect of ambient-temperature drift by using a reference resistor located close to the sensing element but directly on the silicon substrate; and (3) utilizing an optimized novel constant-bias Wheatstone bridge circuit. By choosing a proper bias voltage, which can be found by simple calculation, the circuit extracts information on gaseous thermal conduction from the directly measurable total heat loss of the heated sensing element. The sensor was enclosed in a metal package with a capacity of about 0.5 ml by projection welding and was successfully applied to monitoring the...

Polycrystalline silicon thin films with hydrofluoric acid permeability for underlying oxide etching and vacuum encapsulation

Specialized fabrication techniques created polycrystalline silicon (poly-Si) thin films that were permeable to a concentrated hydrofluoric acid (HF) solution, in order to support in situ vacuum encapsulation of surface microsensor devices on silicon wafers. 0.1-μm-thick poly-Si thin films were made permeable through processes of amorphous silicon film formation by low pressure chemical vapor deposition, successive postannealing for crystallization, and excessive phosphorus diffusion by a phosphorus oxichloride predeposition. Permeability was obtained both on borophosphosilicate glass and nondoped silica glass sacrificial layers. Porous microstructures at the silicon grain boundaries, which were induced by heavy doping of phosphorus and consequent segregation of soluble precipitates, were first observed using a secondary electron microscope and a field emission secondary electron microscope. These observations confirmed that the submicron pores permitted passage of the fluid to dissolve the underlying sacr...

An SOI 3-axis accelerometer with a zigzag-shaped Z-electrode for differential detection

We have developed a fully-differential 3-axis accelerometer with a novel zigzag-shaped Z-electrode, which is used for motion controls of automobiles and robots.

An SOI tactile sensor with a quad seesaw electrode for 3-axis complete differential detection

This paper presents a novel SOI capacitive tactile sensor with a quad-seesaw electrode for 3-axis complete differential detection, which enables integration with a CMOS. For differentially detecting 3-axis forces, the tactile sensor is composed of four rotating plates individually suspended by torsion beams. In this study, to demonstrate the working principle, we fabricated a test device that integrates an SOI substrate with the quad-seesaw electrode and an anodically bondable LTCC substrate with fixed electrodes as an alternative to the CMOS. The experimental results of the test device successfully demonstrated the working principle as well as 3-axis differential detection with a matrix operation.

Anisotropic etching of silicon in (CH/sub 3/)/sub 4/NOH solutions

Detailed characteristics of tetramethyl ammoniumhydroxide, (CH/sub 3/)/sub 4/NOH, as silicon anisotropic etching solutions with various concentrations from 5 to 40 wt.% have been studied. The etch rates of

3-nm gap fabrication using gas phase sacrificial etching for quantum devices

We report nanometer-scale gap (nanogap) fabrication using gas-phase sacrificial layer etching. Sacrificial etching of 3-nm-thick sputtered Si films by XeF/sub 2/ gas was demonstrated for the first time. The same thick Si sacrificial layer was not etched by TMAH solution, and neither HF/CH/sub 3/OH vapor nor BHF solution etched a 3-nm-thick SiO/sub 2/ sacrificial layer. A nanogap formation by etching the 3-nm-thick Si sacrificial layer was ascertained by TEM observations. The underetch depth of a 3-nm gap reached 20 /spl mu/m, which is large enough to use for quantum devices. The etching results were also found to reflect molecular behaviors.

Flipped CMOS-diaphragm capacitive tactile sensor surface mountable on flexible and stretchable bus line

The following novel configuration has been developed for a MEMS-CMOS integrated tactile sensor on a flexible and stretchable bus for covering a social robot body: a sensing diaphragm is formed on a CMOS substrate by backside etching, and the CMOS substrate is flip-bonded to a low temperature co-fired ceramic (LTCC) substrate. By this configuration, no through-silicon vias (TSVs) are needed, simplifying the fabrication process. The flipped CMOS substrate and the LTCC substrate were bonded and electrically connected using Au-Au bonding, which also formed differential capacitive gaps. A flexible and stretchable wire was fabricated by metal etching and polyimide laser cutting. The tactile sensors, which were mounted on the surface of the flexible bus, sent coded digital signals according to applied force.