Self-aligned 0-level sealing of MEMS devices by a two layer thin film reflow process

Many micro electromechanical systems (MEMS) require a vacuum or controlled atmosphere encapsulation in order to ensure either a good performance or an acceptable lifetime of operation. Two approaches for wafer-scale zero-level packaging exist. The most popular approach is based on wafer bonding. Alternatively, encapsulation can be done by the fabrication and sealing of perforated surface micromachined membranes. In this paper, a sealing method is proposed for zero-level packaging using a thin film reflow technique. This sealing method can be done at arbitrary ambient and pressure. Also, it is self-aligned and it can be used for sealing openings directly above the MEMS device. It thus allows for a smaller die area for the sealing ring reducing in this way the device dimensions and costs. The sealing method has been demonstrated with reflowed aluminium, germanium, and boron phosphorous silica glass. This allows for conducting as well as non-conducting sealing layers and for a variety of allowable thermal budgets. The proposed technique is therefore very versatile

The electrolysis of water: An actuation principle for MEMS with a big opportunity

In this paper the theory of water electrolysis in a closed electrochemical cell, that contains two electrodes, an electrolyte and a pressure sensor is described. From the leakage and electrochemical experiments done with this macrocell it is possible to obtain information about the applicability of the electrochemical principle in a closed cavity, the choice of the electrodes and electrolyte, and different types of leakage. To control the pressure of the electrochemical actuator automatically, an electronic feedback system was connected to the cell. A value of the pressure is set and the regulator will actuate the electrochemical cell in such a way to get the desired pressure

New low-stress PECVD poly-SiGe layers for MEMS

Thick poly-SiGe layers, deposited by plasma-enhanced chemical vapor deposition (PECVD), are very promising structural layers for use in microaccelerometers, microgyroscopes or for thin-film encapsulation, especially for applications where the thermal budget is limited. In this work it is shown for the first time that these layers are an attractive alternative to low-pressure CVD (LPCVD) poly-Si or poly-SiGe because of their high growth rate (100-200 nm/min) and low deposition temperature (520/spl deg/C-590/spl deg/C). The combination of both of these features is impossible to achieve with either LPCVD SiGe (2-30 nm/min growth rate) or LPCVD poly-Si (annealing temperature higher than 900/spl deg/C to achieve structural layer having low tensile stress). Additional advantages are that no nucleation layer is needed (deposition directly on SiO/sub 2/ is possible) and that the as-deposited layers are polycrystalline. No stress or dopant activation anneal of the structural layer is needed since in situ phosphorus doping gives an as-deposited tensile stress down to 20 MPa, and a resistivity of 10 m/spl Omega/-cm to 30 m/spl Omega/-cm. With in situ boron doping, resistivities down to 0.6 m/spl Omega/-cm are possible. The use of these films as an encapsulation layer above an accelerometer is shown

Micromachined pipettes integrated in a flow channel for single DNA molecule study by optical trapping

We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap set-up (optical tweezers) to study mechanical and structural properties of λ-DNA molecules. The flow cell was realized using silicon micromachining including the so-called buried channel technology to fabricate the micropipettes, the wet etching of glass to create the flow channel, and the powder blasting of glass to create the fluid connections. The volume of the flow cell is 2 µl. The pipettes have a length of 130 µm, a width of 5-10 µm, a round opening of 1 micron and can be processed with different shapes. Using this flow cell we stretched single molecules (λ-DNA) showing typical force-extension curves also found with conventional techniques

A Medical Microactuator based on a Electrochemical Principle

Glaucoma is a disease causing damage to the optic nerve head due to a too high eye pressure. This damage will lead to visual field loss, and finally to blindness. The current surgery treatment improves the drainage of the eye fluid by introducing a draining device. The problem is that one cannot predict in advance the value of the eye pressure after surgery and it cannot be adjusted to the optimum eye pressure of the patient, after surgery. A continuous adjustment of the eye pressure would simplify and improve the present treatment. The goal of this research is to develop a micromachined actuator that could be combined with existing glaucoma implants. This microactuator, that acts as an active valve would allow the eye pressure to be adjusted continuously around a desired value. The actuator can be used to adjust the eye fluid pressure, for patients suffering from glaucoma, by changing the fluid resistance of an implanted flow channel due to deflection of an integrated membrane. To obtain a low energy consumption and to have the possibility of discontinuous supply of power, it was opted for electrochemical actuation, which is based on the electrolysis of an aqueous electrolyte solution. The reversible electrochemical reactions, which are driven by an external current source, lead to gas evolution or gas reduction (depending on the direction of the current). In a closed system the corresponding gas pressure rise or drop is used to change the deflection of a flexible membrane, which in turn can close or open a liquid channel. If such an electrolytic cell is operated under open-circuit conditions, the pressure and thus the deflection state of the diaphragm will, ideally, be maintained. This means that no energy is required to maintain the state of the valve. It has been proven that relatively large pressures (up to tens of bar) and large deflections can be reached in this electrochemical actuator with a low energy consumption. The complete microactuator system should have a maximum size of 5x5x2 mm3 and will be powered by wireless energy supply. The energy is transmitted by using a pair of coils which are inductively coupled; one coil is implanted and the other one is outside the body

An electrochemical active valve

A novel electrochemical microactuator was developed, which operates as an active valve. The microactuator consists of an electrochemical cell and a membrane that deflects because of the pressure of oxygen gas generated by electrolysis. Relatively large pressures (up to tens of bars) can be reached with only low energy consumption (in the μW range). In a first prototype a Cu/aq. 1 M CuSO4/Pt system was used in an electrochemical cell with dimensions 2×2×1 mm3, fabricated with silicon micromachining and thin film deposition techniques. When the actuator was driven at 1.6 V and currents below 50 μA, pressures of 2 bar could be obtained within seconds, causing membrane deflections in the 30 to 70 μm range. It was found that, in order to improve the performance of the microactuator, it will be necessary to replace the Cu/Cu2+ electrode. A possible alternative is the Sb/Sb-oxide electrode. This system was studied cyclic voltammetry and the first results are promising