Microsystems technology has evolved very fast in the recent past years and its development depends not only on the evolution of process knowledge and manufacturing equipment, but also on the accurate prediction of the behaviour of these systems. Specific modelling and simulation tools for microsystems are required, such as MEMSPro, MEMCAD, Intellisuite or FEMLAB. Their use, however, requires a substantial understanding of the underlying physical behaviour and are computationally intensive since most of them are based on Finite Element Analysis (FEA) methods. Tools based on these methods have widely been used for microsystem modelling and particularly for electric field calculations in electrostatic micromotors. However, the use of system-level languages for modelling and simulating microsystems, can accelerate the design and prototyping phase of microsystems. The standard language VHDL-AMS (VHSIC [Very High Speed Integrated Circuits] Hardware Description Language Analogue Mixed Signal - IEEE 1076.1-1999 standard) has been chosen for developing and simulating our micromotor models. Using VHDL-AMS, all the different sub-elements of a microsystem and the different physical domains involved (electrical, mechanical, fluidic, thermal, etc) can be modelled within the same environment, even at different levels of abstraction. It is also possible to integrate parts of a model constructed or simulated by different means (such as Spice, C language or FEA methods) into the same VHDL-AMS simulation environment, allowing thereby the incorporation of results from previous complex simulations. The work carried out at Heriot Watt University has been focused on modelling the static and dynamic behaviours of two different types of micromotors. The first of them is a variable capacitance (VC) planar electrostatic micromotor designed, fabricated and tested at the Laboratoire d'Analyse et d'Architecture des Systemes (LAAS, Toulouse-France). It is a planar electrostatic device fabricated by a semi-standard surface micromachining process developed in LAAS [1]. The second modelled device is a wobble planar electrostatic motor designed at Heriot Watt University, and fabricate at Cronos (JDS Uniphase, USA) under their Multi-User MEMS Processes (MUMPs) programme [2]. Only experimental measurements for the first kind of motors are presented in this paper. The modelled VC micromotor prototypes have 12 stator electrodes grouped in 3 phases and 8 rotor poles. They have an external diameter of 120 in and an air-gap of 1 to 1.5 in between rotor and stator. A SEM photograph and an schematic with the micromotor geometrical dimensions presented in Figure 1. The electrostatic forces generated between the grounded rotor and the activated stator electrodes are the basis of the operation of VC electrostatic micromotors. DC voltages in the range of 0..200 V are applied to 4 electrodes at a time (1 phase) and the three excitation phases are switched on and off making the rotor spin continuously. Different excitation schemes can be applied to the stator, resulting in different motor performances. The objective of the work presented here is to create a simple and accurate model of the micromotor in order In conclusion, good agreement has been found between the proposed micromotor model simulation results and the collected experimental data. A better understanding of friction modelling issues has also been achieved through iterative simulation. Developed VHDL-AMS blocks can be considered as an initial phase towards the creation of Intellectual Property (IP) blocks for microsystems in general and electrostatic micromotors in particular, enabling MEMS design reuse and exchange between different designer teams. These blocks can subsequently be used for high level simulation of different types of systems along with other electronic or mechanical blocks, all within the same standard framework provided by VHDL-AMS. Experimental data from the MUMPs fabricated wobble micromotors will be presented in a future along with their VDHL-AMS models.
