Improved design of micromachined lateral suspensions using intermediate frames

Abstract

A complete analysis of the translational and rotational modes of a model lateral suspension is presented. The derived formulae quantify spurious-mode resonant frequencies for cross-axis translation and rotation, and on-axis translation, and can provide very simple expressions for the rejection ratios in terms of the geometry of the suspensions. It is shown that the introduction of intermediate frames, coupling equivalent points of the lateral suspension either side of the suspended mass, can provide much improved dynamics. To investigate the derived relationships, suspensions have been fabricated using through-wafer deep reactive-ion etching (DRIE). Using analysis of the suspension dynamics under the rastered beam of a scanning electron microscope, the various modes of the suspension have been visualized and quantified. These observations are in good agreement with the derived formulae, taking into account the actual profile of the beams fabricated in DRIE. Further finite element analysis across a broad range of suspensions is consistent with the derived formulae. A design heuristic is provided for rapidly optimizing micromachined lateral suspensions by incorporating intermediate frames.

A self-levelling nano-g silicon seismometer

“…The geometry of the lateral suspension has been selected [4] to produce a fundamental vibrational mode in the plane of the wafer of between 6 and 12 Hz with maximum cross-axis stiffness in a 20 to 25mm die.…”

Highly linear and large spring deflection characteristics of a Quasi-Concertina MEMS device

“…The design of the QC spring, shown in Fig. 1a, is based on using a number of beams in series to increase the linear and deflection range beyond the thickness of beam used [1], and on the mechanical behaviour of beams in which the compliance of a beam in tension or pre-buckling compression is much less than that of the same beam in bending [8]. Using these guidelines, a platform was suspended with beams oriented such that a relatively low spring constant, high linear range, and high deflection range was achieved in the z out-of-plane direction.…”

“…The spring in accelerometers [1], gyroscopes [2], optical mirrors [3], and biosensors [4] is a critical component that affects the overall accuracy, output linearity, and operation range of such micro electromechanical systems (MEMS) devices. The basic spring types used in MEMS are the cantilever, double clamped beam, hammock, crableg, and the folded spring [5].…”

“…The basic spring types used in MEMS are the cantilever, double clamped beam, hammock, crableg, and the folded spring [5]. However, in circumstances where a large linear and travel range is required a serpentine spring [6] is typically used, and a lateral suspension [1] is used when the inplane compliance also needs to be much greater than the out-of-plane compliance. For applications that require the out-of-plane compliance to be much greater than the in-plane compliance, the spring-supported diaphragm [7] would be a suitable choice for small deflections; however, there is still little work done on a flexure type spring that can in addition also give a high linear and large deflection range in the out-of-plane direction.…”

Sensor Fusion Methodology to Overcome Cross-Axis Problem for Micromachined Thermal Gas Inertial Sensor

“…Like most axis-sensitive sensors, such as accelerometers [11] and magnetometers [12], the thermal gas inertial sensor inevitably undergoes the cross-axis problem [13], which generally causes serious errors in measurements. The common strategy to overcome the cross-axis problem for a micromachined sensor is to adopt a tailored complex structure design to diminish the coupling effect among cross-axes [14], [15], and thus brings complex fabrication. In this paper, we will propose a fusion methodology to overcome the cross-axis problem for realizing multiaxial rotation measurements.…”