Oliver Paul

Novel 3D piezoresistive silicon force sensor for dimensional metrology of micro components

This paper reports the successful fabrication and characterization of a novel three-axial silicon force sensor based on piezoresistive transducers and its application in dimensional metrology. The innovative sensor design enables a distinct reduction of the critical ratio Sz /Sx of out-of-plane stiffness Sz to in-plane stiffness Sx. In contrast to existing single-chip sensors with Sz/Sx = 30 a ratio of 4 is achieved which improves the detection of inclined surfaces. The sensor consists of a flexible cross-structure realized by deep reactive ion etching. The arms of the cross-structure are connected to a silicon frame and to the central part of the cross-structure through silicon membranes hinges. A stylus with a probing sphere is used as the tactile element. Forces applied to the sphere are transferred into a deflection of the cross-structure. The respective stress values in the membranes are detected using implanted piezoresistors. The sensor element is applied in dimensional metrology of micro components with lateral dimensions larger than 100 mum. The lateral resolution of the sensor element is 10 nm

Electrostatic Transducers for Micro Energy Harvesting Based on SOI Technology

This paper describes the modeling, fabrication, and characterization of SOI-based micro- electro-mechanical transducers used for energy harvesting. The electrostatic transducers convert vibrations of a seismic mass by means of variable capacitors realized using comb structures. The seismic mass with comb electrodes is suspended by four 1-mm-long straight beam springs. Transducers with springs of different widths with theoretical resonance frequencies ranging from 96 to 1160 Hz were realized. The frequency behavior of the resonators is investigated using an in-plane vibrometer with nm resolution. Linear and non-linear responses are measured for weak and hard driving excitations, respectively. The effect of the capacitance variation on the harvested power is investigated as well as the application of different resistive loads to the devices.

Piezo-hall effect in CMOS-based vertical hall devices

This paper reports on the piezo-Hall effect in CMOS-based five-contact vertical Hall sensors (VHS) able to measure in-plane magnetic field components. The geometry of such devices and the characteristic current flow in the deep n-wells strongly differ from those of structures used so far to characterize the piezo-Hall response. In contrast to standard planar Hall plates, homogeneous mechanical in-plane stress was found to cause a weak change in the magnetic sensitivity of the VHS. The paper presents the custom-made measurement setup and its detailed characterization as well as experimental results acquired using single VHS and coupled sensor systems comprising four VHS connected in parallel. The experimental results are supported by finite element simulations. It is concluded, that the low sensitivity change is due to the vertical current density changes induced by the applied mechanical stress.

On the influence of thermal treatment on strain sensors based on the ferromagnetic shape memory alloy NiMnGa

This paper presents a novel concept for improving the performance of mechanical sensors based on the ferromagnetic shape memory alloy NiMnGa. It is shown that a pseudo-plastic deformation that occurs during sensor operation can be fully reversed by heating the magnetic shape memory (MSM) element above its martensite-to-austenite transition temperature and by subsequently cooling it down to room temperature in a moderate external magnetic bias field. This represents an essential feature for future sensor applications as it eliminates the necessity for a strong magnetic bias field. It can therefore help to miniaturize MSM-based mechanical sensors and even increase their sensitivity. This paper presents an initial proof-of-concept using a custom made test setup.

CMOS tactile sensor systems

Tactile sensor systems based on complementary metal-oxide-semiconductor (CMOS) technologies have found a wide variety of applications covering various types of man-machine interfaces as well as industrial applications. These sensor systems are realized using commercially available CMOS processes combined with appropriate assembly technologies for advanced system packages, and dedicated micromachining processes to realize membranes or beam structures to improve the sensor sensitivity. Piezoresistive CMOS-based tactile sensor systems make use of implanted resistors and field-effect transistors (FETs) exploiting the piezoresistive effect in silicon. The applied CMOS chips extract the mechanical stress distribution in the chip surface which is characteristic for the corresponding mechanical loading of the CMOS chip or its package. This paper describes a three-dimensional force sensor used in metrology to extract the 3D geometry of precision machined parts, and the Smart Tooth, an innovative tool for orthodontic research and education.