MEMS Sensor for In Situ TEM Atomic Force Microscopy

Here, we present a MEMS atomic force microscope sensor for use inside a transmission electron microscope (TEM). This enables direct in situ TEM force measurements in the nanonewton range and thus mechanical characterization of nanosized structures. The main design challenges of the system and sensor are to reach a high sensitivity and to make a compact design that allows the sensor to be fitted in the narrow dimensions of the pole gap inside the TEM. In order to miniaturize the sensing device, an integrated detection with piezoresistive elements arranged in a full Wheatstone bridge was used. Fabrication of the sensor was done using standard micromachining techniques, such as ion implantation, oxide growth and deep reactive ion etch. We also present in situ TEM force measurements on nanotubes, which demonstrate the ability to measure spring constants of nanoscale systems.     

Replication of continuous-profiled micro-optical elements for silicon integration

A novel scheme for the integration of diffractive optical elements onto silicon is presented. The processing is made in reverse order, meaning that the process of structuring the optical elements on the wafer precedes the silicon microstructuring. The first processing step on the wafer is the hot embossing of the optical microstructures into an amorphous fluorocarbon polymer spin coated on the wafer. The cured polymer forms a highly stable material with excellent optical properties. The remaining silicon processing is thus performed with the diffractive optical elements already in place. Two different diffractive structures were used in the development of the method-a (Fresnel) lens with a rather low f-number and a diffractive element producing a fan-out of a large number of paraxial beams.     

Micromachined flat-walled valveless diffuser pumps

The first valveless diffuser pump fabricated using the latest technology in deep reactive ion etching (DRIE) is presented. The pump was fabricated in a two-mask micromachining process in a silicon wafer polished on both sides, anodically bonded to a glass wafer. Pump chambers and diffuser elements were etched in the silicon wafer using DRIE, while inlet and outlet holes are etched using an anisotropic etch. The DRIE etch resulted in rectangular diffuser cross sections. Results are presented on pumps with different diffuser dimensions in terms of diffuser neck width, length, and angle. The maximum pump pressure is 7.6 m H₂O (74 kPa), and the maximum pump flow is 2.3 ml/min for water     

Vibration modes of a resonant silicon tube density sensor

We present an investigation of the resonance parameters for a new sensor for on-line measurements of fluid density. The sensor consists of a tube system made of single crystalline silicon. The tube system is excited electrostatically into mechanical resonance and the vibration is detected optically. Using a simplified theoretical analysis, the resonance frequency can be shown to be proportional to 1√ρ, where ρ is the density of the silicon and the fluid weighted according to their areas in a cross section of the tube. Thus, a change in fluid density results in a change in the resonance frequency. This dependence is demonstrated by measurements for four different vibrations modes. The quality of the vibration is also investigated through measurements of the Q-values of the vibration modes. The tubes are made using anisotropic silicon KOH etching and silicon-to-silicon fusion bonding micromachining techniques. The dimensions of the tube system are 8.6×17.7 mm with an outer tube thickness of 1 mm and a wall thickness of 100 μm. Total tube length is 61 mm, and the sample volume is 0.035 ml. The sensor has a very good density sensitivity of the order of -200 ppm/(kgm^-3) and a high Q of the order of 3000 for air in the tube