The development towards smaller devices with more functions integrated calls for new and improved manufacturing processes. The screen-printing process is quite well suited for miniaturised and integrated devices, since thick films can be produced in this manner without the need for further machining. On the other hand, the process of screen printing thick films involves potential problems of thermal matching and chemical compatibility at the processing temperatures between the functional film, the substrate and the electrodes. As an example of such a miniaturised device, a MEMS accelerometer based on PZT thick film will be presented. The design and process flow of this accelerometer has been optimised by means of finite element modelling (FEMLAB©). Consequently it has proved possible to eliminate post-processing steps after the screen printing of the PZT thick film.

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Piezoelectric thick films have increasing interest due to the potential high sensitivity and actuation force for MEMS sensors and actuators. The screen printing technique is a promising deposition technique for realizing piezoelectric thick films in the thickness range from 10-100 μm. In this work integration of a screen printed piezoelectric PZT thick film with silicon MEMS technology is shown. A high bandwidth triaxial accelerometer has been designed, fabricated and characterized. The voltage sensitivity is 0.31 mV/g in the vertical direction, 0.062 mV/g in the horizontal direction and the first mode resonance frequency is 11 kHz. A Finite Element Method (FEM) model is used to validate the measured sensitivity and resonance frequency. Good agreement between the model and the measurements is seen.

Laplace photoinduced transient spectroscopy has been applied to determine the electronic properties and concentrations of deep traps in high purity n-type silicon irradiated with high fluences of 23-MeV protons. From the temperature dependence of thermal emission rates of excess charge carriers obtained by the analysis of the photocurrent relaxation waveforms measured at temperatures of 30–320 K, eight deep traps with activation energies ranging from 255 to 559 meV have been resolved. The dependence of these trap’s concentrations on the proton fluence are demonstrated for the fluence values ranging from 1 × 1014 to 5 × 1015 neq/cm2. In comparison to the previously reported results of theoretical and experimental studies on the electronic properties of small vacancy clusters in irradiated silicon, we tentatively attribute four detected traps with activation energies of 255, 367, 405, and 512 meV to the energy levels related to the 2−/− charge state changes of divacancy (V2), trivacancy (V3), tetravacancy (V4), and pentavacancy (V5), respectively. Simultaneously, we propose the attribution of four deep traps with higher activation energies of 415, 456, 526, and 559 meV to the energy levels related to the −/0 charge state changes of these small vacancy clusters, respectively.

Abstract-We present a mechanical model of a triaxial micro accelerometer design using PZT thick-film as the sensing material. The model is based on the full anisotropic material tensors and Eulers' beam equation using simplifying assumptions where the smaller stress contributions are ignored. The model results in design equations that are useful for optimization of the sensitivity and bandwidth and for matching the sensitivity in the three orthogonal directions. A finite-element method (FEM) model is used to verify the analytical model. Equal sensitivity in all three geometrical directions is preferred, which induces a number of limitations in design parameter space, this is used in a design strategy for setting the six independent dimensions of the accelerometer. Design methods for optimum sensitivity of each axis and for equal sensitivity between different axes have been proposed.