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The phenomenon and the mechanisms of silicon to silicon direct bonding have been thoroughly studied. 1-4 Nevertheless, there is still a need for reliable evaluation methods to determine the quality of a bond due to different treatments. The widely used crack opening method, introduced by Maszara, is a fast and convenient method to determine the surface energy of a bond. 1 This technique is well suited to study bond mechanisms and surface chemistry, as the surface energy is the most relevant quantity characterizing these phenomena. However, there are severe problems connected to the crack opening technique, i.e., inaccuracy, insecure operator dependence, and the impossibility for its use on too strong bonds.The fracture strength of bonds needs to be evaluated in order to obtain mechanically reliable silicon microstructures. In this work, a new strategy toward a robust evaluation method is presented. It is based on fracture probability measurements on directly bonded structures. The strength of components, manufactured from brittle materials, depends on the combination of defect and stress distribution. When the stress around a defect reaches a critical level, fracture is initiated. If the stress is well defined and known, the fracture strength can be determined by the distribution of defects. This paper suggests a method to indirectly estimate the defect distribution at the interface of bonded silicon wafers. Thus, when the strength of a component is limited by the bond, the problem of finding the strength will be the problem of finding the stress distribution at the bonded interface. By the Weibull fracture probability analysis, it is hereafter possible to derive geometry-independent parameters, which makes comparisons and predictions of the fracture behavior for differently shaped and sized structures possible. The advantage of this method is that it applies to whole bonded wafers as well as to bonded micromachined components. Experimental All bonded structures were made from single-side polished 100 mm diam silicon wafers, 525 m thick. Bonded pairs with a cavity in one wafer and a gas inlet in the other were made. Series of these modules were burst, by applying a gas pressure between the bonded wafers. The resulting bond fracture probability was determined and correlated to different treatments and characteristics such as annealing temperature, cavity size, thermal cycling, and vibration tests. According to the theory below, the cavity depth is negligible to the bond fracture probability when it is kept sufficiently small, and it was arbitrarily chosen to 30 m. All structures were made by anisotropic wet etching in KOH. The wafers were bonded using hydrophilic fusion bonding 3 and hot nitric acid surface treatment prior to contacting. They were annealed until saturated bond strength values were reached: 90 h at 120 and 300ЊC, 5 and 3 h at 700, 800, and 1050ЊC.Two test series were subjected to one of the fatiguing procedures of vibration or thermal cycling, respectively. The fatiguing test parameters are given i...

Purpose -The purpose of this paper is to describe the collective exploration, process and knowledge production made in a learning study about solution chemistry. Design/methodology/approach -Secondary school teachers conducted a learning study with variation theory as a guiding principle, supervised by a researcher. The relationship between teaching and learning was analyzed and evaluated in a learning study cycle of three lessons. Findings -Critical aspects when teaching solution chemistry were identified, as well as enacted patterns of variation that significantly improved students' learning. Examples of critical aspects were the particulate character of matter, especially the feature of "empty space" between particles, the connection between macroscopic phenomenon and sub-microscopic explanations and the difference between answers with everyday language and scientific language. Practical implications -The paper suggests that teachers in a learning study can produce new knowledge as well as use earlier research results when creating teaching activities that can improve their own practical work and students' learning. Originality/value -The study represents an example of research with the aim to improve teachers' practice by generating knowledge in connection with teachers' professional tasks.

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Development of a MEMS-based (Micro Electro Mechanical System) components and subsystems has been pursued at Uppsala University, Sweden since 1997. Since 2005, the continued development towards the first flight the subject MEMS products onboard a satellite in 2008 is done within the frame of NanoSpace — a company dedicated to MEMS-based products for space. Currently, two major efforts to develop MEMS-based propulsion products are ongoing. First, NanoSpace is developing a miniaturized cold gas propulsion system. The major challenge in this effort is to develop the thruster module containing four individual thrusters with the capability to deliver proportional, low noise thrust in the micro- to milli-Newton range. The thruster pod even includes valves, filters, pressure- and temperature sensors and heaters. In a future step, even control electronics and a CAN interface will be included in the thrusters pod which has the size of a golf ball and a weight of about 100 grams. A prototype of this miniaturized cold gas propulsion will be flight tested onboard the PRISMA satellite. PRISMA is an international technology demonstration program with focus on rendezvous and formation flying. It is a two satellite LEO mission with a launch scheduled to September 2008. The other major development effort underway is a MEMS-based Xenon flow control system intended for electrical propulsion systems. Using MEMS technology, a Xenon feed system including an micro isolation valve, pressure regulator, and a number of parallel flow control modules can be built with significantly reduced size and mass compared to existing systems based on conventional technology. NanoSpace is a Swedish company with the goal to be a component and subsystem supplier of MEMS-based products to space industry, based on own research and development and intellectual property rights.