An intensive study has been performed to understand and tune deep reactive ion etch (DRIE) processes for optimum results with respect to the silicon etch rate, etch profile and mask etch selectivity (in order of priority) using state-of-the-art dual power source DRIE equipment. The research compares pulsed-mode DRIE processes (e.g. Bosch technique) and mixed-mode DRIE processes (e.g. cryostat technique). In both techniques, an inhibitor is added to fluorine-based plasma to achieve directional etching, which is formed out of an oxide-forming (O 2) or a fluorocarbon (FC) gas (C 4 F 8 or CHF 3). The inhibitor can be introduced together with the etch gas, which is named a mixed-mode DRIE process, or the inhibitor can be added in a time-multiplexed manner, which will be termed a pulsed-mode DRIE process. Next, the most convenient mode of operation found in this study is highlighted including some remarks to ensure proper etching (i.e. step synchronization in pulsed-mode operation and heat control of the wafer). First of all, for the fabrication of directional profiles, pulsed-mode DRIE is far easier to handle, is more robust with respect to the pattern layout and has the potential of achieving much higher mask etch selectivity, whereas in a mixed-mode the etch rate is higher and sidewall scalloping is prohibited. It is found that both pulsed-mode CHF 3 and C 4 F 8 are perfectly suited to perform high speed directional etching, although they have the drawback of leaving the FC residue at the sidewalls of etched structures. They show an identical result when the flow of CHF 3 is roughly 30 times the flow of C 4 F 8 , and the amount of gas needed for a comparable result decreases rapidly while lowering the temperature from room down to cryogenic (and increasing the etch rate). Moreover, lowering the temperature lowers the mask erosion rate substantially (and so the mask selectivity improves). The pulsed-mode O 2 is FC-free but shows only tolerable anisotropic results at −120 • C. The downside of needing liquid nitrogen to perform cryogenic etching can be improved by using a new approach in which both the pulsed and mixed modes are combined into the so-called puffed mode. Alternatively, the use of tetra-ethyl-ortho-silicate (TEOS) as a silicon oxide precursor is

A detailed study is performed to understand and show the potential of high-speed, deep reactive ion etching (DRIE) of silicon using oxygen inhibitor pulses as a replacement for hydro-fluorocarbons (HFCs). This process might be considered the 'holy grail' in DRIE as the environmental restrictions for the use of HFCs are becoming increasingly stronger. When compared to the usual cryogenic mixed oxygen DRIE and with respect to profile control, the proposed cryogenic pulsed oxygen DRIE is virtually independent of silicon loading, mask material and trench width, and it is less prone to the formation of black silicon (BS). Some indication is found that one of the major causes for the formation of BS is the existence of dust inside the plasma. Dust is created when oxygen and silicon tetra fluoride (SiF 4 being the reaction product of silicon etching) coincide inside the plasma glow. This occurs in mixed oxygen plasma; the silica dust falls onto the wafer where it starts to form BS when directional etching is requested. Dust particles can also form when strong polymerizing gases are fed into the plasma. This is the case for the Bosch process using HFC pulses forming carbonic dust. The particles, and consequently the BS, are observed to be limited when the SiF 4 and O 2 gases are time separated, which forms the basis of the proposed pulsed oxygen DRIE. Another advantage of pulsed oxygen DRIE with respect to Bosch processing is that the protective skin of the sidewall during etching-a kind of native oxide-is believed to be self-terminating. This makes the process insensitive to profile variations caused by parameter fluctuations. It is found that inhibiting oxygen pulses give excellent results with respect to profile control at cryogenic temperatures (between −120 and −80 • C) and can still compete with HFC pulses up to intermediate low temperatures (between −80 and −40 • C). When selecting the proper DRIE conditions, the oxygen pulsed mode performs with excellent profile verticality and selectivity while keeping the silicon clean. It also shows a high etch rate up to 25 μm min −1 (<1% Si load of a 100 mm wafer). When the temperature is raised further (between −40 and 0 • C), the strength of the oxygen sidewall protection progressively fails and more oxygen with more bias is needed to keep sufficient profile directionality. The use of stronger oxide-forming agents is suggested in order to enable good performance at the more convenient, higher temperature, low bias conditions.

To enable formation flying of micro satellites, small sized propulsion systems are required. Our research focuses on the miniaturization of a feeding and thruster system by means of micro system technology (MST). Three fabrication methods have been investigated to make a conical converging-diverging nozzle. These methods are reactive ion etching, femtosecond laser machining (FLM) and a combination of powderblasting and heat treatment. It is shown that the latter two methods are very promising.

In this paper, we present the design, fabrication and characterization of a novel gas microvalve realized by combining micro-and fine-machining techniques. The design is for high flow rates at high pressure difference between inlet and outlet, burst pressure of up to 15 bars. There is no power consumption required for the valve to maintain its position during operation in any intermediate state and the process gas does not interact with the actuation mechanism. The microvalve was experimentally characterized with air flows. It is shown that flow rates of 220 ml min −1 at a pressure difference of 4 bars could be achieved with a minimum accurate flow rate of 4 ml min .

We propose a novel concept for a high-speed optical data link in 360 µm diameter cardiovascular interventional imaging guidewires. The concept is based on the recently introduced Flex-to-Rigid (F2R) technology platform. This technology allows for new intravascular imaging devices with the required small form-factor. We extended the existing F2R technology with a new optical data link assembly method to enable high speed data communication from the distal tip of the catheter to the proximal side. In this method, the fiber is aligned by inserting it into a through-wafer hole directly underneath the flip-chipped Vertical-Cavity-Surface Emitting Laser (VCSEL). Therefore, the total diameter of the optical data link is primarily limited by the size of the VCSEL. A wafer-scale demonstrator setup was fabricated with a commercially available 350x250 µm VCSEL and an 80 µm diameter multimode optical fiber. Test results of our demonstrator showed a correct optic coupling of the VCSEL into the fiber.