In-plane Accelerometer Research Articles

Quarter-mm2 High Dynamic Range Silicon Capacitive Accelerometer With a 3D Process

A new 3D process is proposed for inertial MEMS sensors where a thin transduction layer based on high-density surface-varying comb fingers, with nano-metric gaps, is patterned below a thick seismic mass layer. The objective is to achieve high-performance in a reduced footprint. An in-plane accelerometer is designed, fabricated with this new 3D process, and tested under acceleration. Initial fabricated devices demonstrate a full-scale range of ±160 g, $7~\mu {g}/ \sqrt {\textit {Hz}}$ Brownian noise floor and more than 4 kHz bandwidth. These figures translate into a dynamic range of more than 150 dB (normalized to 1-Hz bandwidth) with an overall footprint of only ${400}\times {600}\,\,\mu {m}^{{2}}$ .

Self-powered In-plane Accelerometer Using Triboelectric Mechanism

This paper presents a self-powered triboelectric based accelerometer to detect wide range of in-plane acceleration utilizing the triboelectric mechanism. The freestanding sliding mode was utilized to realize the in-plane sensing. The fabricated device consists of soft polymer spring which displays wide detection range from ±1g to ±6g (g = 9.8m/s2) in x and y directions with sensitivity of 21mV/(g). The proposed device can be utilized for self-powered shock sensing in various future applications.

Monolithic CMOS—MEMS Pure Oxide Tri-Axis Accelerometers for Temperature Stabilization and Performance Enhancement

A complementary metal–oxide–semiconduc-tor (CMOS)–microelectromechanical system (MEMS) accelero-meter with stacked pure oxide layers as mechanical structures was developed. Metal layers were confined to the sensing electrodes and electrical routings; the metal–oxide composite in the CMOS–MEMS accelerometer was distributed in limited regions. This design has two major advantages: 1) the thermal deformation of suspended MEMS structures resulting from a mismatch in the coefficients of thermal expansion of the metal and the oxide in the metal–oxide films is suppressed; and 2) the parasitic capacitance of the sensing electrode routing underneath the proof mass is reduced. Thus, the accelerometer has higher sensitivity and reduced thermal drift. The curvature of the mechanical structures are improved in the temperature span and the noise floor is lowered. In the full temperature span (30 °C–90 °C), change in the radius of curvature per unit change in the temperature was 0.08%/°C for the in-plane accelerometer and 0.37%/°C for the out-of-plane accelerometer. Compared with the typical metal–oxide design, the proposed pure oxide design yielded a >20-fold improvement in radius of curvature change per unit temperature change for the in-plane accelerometer and a fivefold improvement for the out-of-plane accelerometer. Moreover, the noise floor was reduced to 0.40 ( $x$ -axis), 0.21 ( $y$ -axis), and 0.94 mG Hz $^{-1/2}$ ( $z$ -axis), respectively, a 2.2–7.6-fold improvement compared with the metal–oxide design. [2015-0012]

Design and Testing of In-Plane MEMS High-g Accelerometer

μAiming at the demand of missile fuse and other weapons systems, a high-g piezoresistive accelerometer with two terminal fixed beam-mass structure which can measure in-plane acceleration was designed. The design and simulation were also performed using Matlab and ANSYS. The simulation results show that the sensitivity of the accelerometer of sensitive-axis is 0.1101μV/g, and the transverse sensitivity of accelerometer is eliminated effectively. The key parameters such as impact over-loading signal and sensitivity of in-plane accelerometer were tested by Master hammer and Hopkinson bar. The test results showed that the sensor can work with the impact acceleration up to 117,395.95 g and the sensitivity of the accelerometer is 0.1028μV/g.

Compact electrode design for an in-plane accelerometer on SOI with refilled isolation trench

A two-axis in-plane capacitive accelerometer containing a refilled isolation trench is fabricated in 50 µm silicon-on-insulator (SOI). In the accelerometer, each stationary electrode is split into two sub-stationary electrodes by the refilled isolation trench, and the two sub-stationary electrodes form a pair of differential capacitors with the adjacent movable electrodes. With this deployment, there is no necessity to keep a wide gap between the split stationary combs to avoid stiction, and the sensing electrodes are arranged compactly. Compared with a typical design without isolation trench across the stationary comb, the presented accelerometer allows more pairs of differential capacitors arranged in a given sensing area, and thus has higher capacitance sensitivity. Experimental results show that the capacitance sensitivity is 0.19 pF g−1 and nonlinearity is 0.4%. In addition, the overlap area-changed capacitor enables the accelerometer to reduce the damping coefficient and minimize the possibility of stiction.

New capacitive low-g triaxial accelerometer with low cross-axis sensitivity

This work describes a compact accelerometer, which integrates three spring-proof mass systems into a single structure to sense triaxial motion. It has a size of 1.3 × 1.28 mm2 and an operating range of ±1 g. Silicon-on-glass (SOG) micromachining and deep reactive-ion etching (DRIE)-based process are adopted to fabricate this accelerometer with a high-aspect-ratio sensing structure. The accelerometer has an excellent z-axis output sensitivity of 1.434 V g−1 and a high resolution of 49 µg Hz−1/2. The sensitivity and minimum cross-axis sensitivity of the x-axis in-plane accelerometer are 1.442 V g−1 and 0.03% and those of the y-axis accelerometer are 1.241 V g−1 and 0.21%, respectively. The new in-plane and out-of-plane accelerometer design exhibits high cross-axis sensitivity immunity, high sensitivity and high linearity suggesting that the triaxial accelerometer has the potential for use in future applications in consumer goods and the cellular phone market.

Sub-Micro-Gravity In-Plane Accelerometers With Reduced Capacitive Gaps and Extra Seismic Mass

This paper presents a robust fabrication technique for manufacturing ultrasensitive micromechanical capacitive accelerometers in thick silicon-on-insulator substrates. The inertial mass of the sensor is significantly increased by keeping the full thickness of the handle layer attached to the top layer proof mass. High-aspect-ratio capacitive sense gaps are fabricated by depositing a layer of polysilicon on the sidewalls of low aspect- ratio trenches etched in silicon. Using this method, requirements on trench etching are relaxed, whereas the performance is preserved through the gap reduction technique. Therefore, this process flow can potentially enable accelerometers with capacitive gap aspect-ratio values of greater than 40:1, not easily realizable using conventional dry etching equipment. Also, no wet-etching step is involved in this process which in turn facilitates the fabrication of very sensitive motion sensors that utilize very compliant mechanical structures. Sub-micro-gravity in-plane accelerometers are fabricated and tested with measured sensitivity of 35 pF/g, bias instability of 8 mug, and footprint of <0.5 cm2.

Fabrication of a new highly-symmetrical, in-plane accelerometer structure by anisotropic etching of (100) silicon

In this paper, we present a silicon bulk-microfabrication method which helps to overcome simultaneously several limitations of multi-axis micro-accelerometers. The method demonstrates an orginal solution to the building of a symmetrical structure by using double-side wet etching. This is a low-cost alternative to existing techniques for the fabrication of highly-symmetrical, single crystal silicon structures. The proposed approach provides low mechanical cross-sensitivities as well as the possibility of a batch fabrication process of the whole three-dimensional device without loss of accuracy due to assembly operation. For the fabrication of thin suspended beams with vertical sidewalls, a non-conventional alignment of from the wafer flat was used. This alignment allows one to fabricate two perpendicular devices on one wafer in the same etching step. The etching was performed with a simple standard wet etching process in a KOH solution. A number of structures were fabricated to demonstrate the feasibility of this method. Aspect ratios (beam height over beam thickness) of over 35 were easily achieved. Undercut directions were determined and design rules for the mask layout were established. To describe the mechanical behaviour of the fabricated structure, an analytical model was implemented and a finite-element simulation was performed. First measurements of the seismic mass displacement were performed with an optical comparator, and they agree with theoretically obtained results. The new design offers the possibility of a two-axis accelerometer system on one wafer, consisting of two sensor elements rotated by . A three-axis monolithic accelerometer system with intrinsic perpendicular alignment due to the rectangular symmetry of the (100) planes can be realized, by including a third sensor element sensitive to vertical accelerations.