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Aspect ratios up to several 10 4 can be reached. The pressure dependence of the performance of resonant MEMS devices, like resonators and gyroscopes, is the result of damping effects. The equation of motion is: The chemical nature of this etching process provides a good selectivity, which means the etching rate of the target material is considerably higher than the mask material if selected carefully. A pressure sensor to test the cavity vacuum of MEMS resonators in batch production should therefore mems pressure sensor pdf download more sensitive to the lower pressures than the HF timing device itself.
For some applications, the separation is preceded by wafer backgrinding in order to reduce the wafer thickness. The thermal resistance of the suspended supports is due to mems pressure sensor pdf download silicon. However, the motional resistance of mechanical resonators is not very stable over time, which makes these sensors unreliable in measuring absolute pressure over time, particularly low pressures.
In one example, separate resonator elements can be used; one for the MEMS device e. The resonant frequency is used for sensing the pressure, and this resonant frequency can be in the range of several hundreds of kilohertz or lower.
The use of the term mems pressure sensor pdf download for plasma etching should not be conflated with the use of the same term when referring to orientation-dependent etching. Therefore, the pressure sensor device is not critical to the damping by the mechanical springs. A device as claimed in claim 11wherein a single MEMS resonator element is controlled to vibrate in a lateral mode to function as the device resonator element, and is controlled to vibrate in a vertical resonant mode to function as the pressure sensor resonant element.
A Framework for Calibration of Barometric MEMS Pressure Sensors – ScienceDirect
The resonant frequency can be read out by piezo-resistive, capacitive or optical sensing methods. Digest of Technical Papers. Electrostatically-actuated structures for fluid property measurements and related methods.
A long exposure time leaves the user vulnerable to beam drift or instability which may occur during the exposure. Proceedings of the IEEE. It should further be integrated in the MEMS micro cavity if possible. This avoids having a second MEMS device in the same micro cavity. The device will not be damaged if suddenly exposed to 1 atmosphere approx 1 kPaunlike current membrane pressure sensors for the 1 mbar range. mems pressure sensor pdf download
This invention is based on a different monitoring mechanism which affects the resonance frequency. In the latter, the material is sputtered or dissolved using reactive ions or a vapor phase etchant. Plasma etching can be isotropic, i. In combination with wet anisotropic etching as described above, ECE has been used successfully for controlling silicon mems pressure sensor pdf download thickness in commercial piezoresistive silicon pressure sensors. Low carbon steel sheet, Low carbon steel cast piece and method for production thereof.
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Currently there are two variations of the DRIE. Plasma etchers can operate in several modes by adjusting the parameters of the plasma.
The sensor can be used for sensing external pressure in the range of 0. By defining a current through the device, passing via the anchors through the resonator, the resonator becomes heated. Essentially there are mems pressure sensor pdf download possible approaches: The surface of these grooves can be atomically smooth if the etch is carried out correctly, with dimensions and angles being extremely accurate.
Interdigital comb electrodes were used to produce in-plane forces and to mems pressure sensor pdf download in-plane movement capacitively. The invention is based on the link between the damping force and the pressure, and the effect of the resulting change in spring constant on the resonant frequency. The steeper the slope of fractional change versus pressure, the easier the determination of pressure.
Wafer dicing may then be performed either by sawing using a cooling liquid or a dry laser process called stealth dicing.
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By the sensitivity of FIG. If the ions have mems pressure sensor pdf download enough energy, they can knock atoms out of the material to be etched without a chemical reaction. It was developed for manufacturing integrated circuitsand is also used for creating nanotechnology architectures.
Preferably, narrow etch slits and plate perforations are used to prevent the gas from escaping the resonator gap during the oscillations. The pressure sensor of the invention is compatible with many microstructure layouts. The resonant frequency depends on the gas pressure, so that the resonator beam can be used as a Pirani element, particularly suitable for use at high pressures.
Microelectromechanical systems – Wikipedia
To excite the vertical resonant mode, a top electrode is provided in addition to the lateral drive electrodes for the bulk mode. It can be assumed that the mean free path of the gas molecules is larger than the device dimensions, i.
The purpose, as with photolithography semsor, is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching. MEMS became practical once they could be fabricated using modified semiconductor device fabrication technologies, normally mems pressure sensor pdf download to make electronics. This shows that at higher pressures, amplitude monitoring may be preferred in addition mems pressure sensor pdf download or instead of frequency monitoring.
Thus, senslr can be estimated from an amplitude measurement. The patterns can be formed by selective deposition through a silicon dioxide mask, or by deposition followed by micromachining or presure ion beam milling. The possible miniaturisation and low cost means that redundancy can be built in to a sensor head where maintenance is limited, such as in nuclear or space applications.