JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 23, NO. 4, AUGUST 2014 871 Improving the Sensitivity and Bandwidth of In-Plane Capacitive Microaccelerometers Using Compliant Mechanical Amplifiers Sambuddha Khan, Student Member, IEEE, and G. K. Ananthasuresh Abstract—This paper presents a method to enhance both the sensitivity and bandwidth of in-plane capacitive microma- chined accelerometers by using compliant mechanical amplifiers, and thus obviating the compromise between the sensitivity and bandwidth. Here, we compare one of the most sensitive single-axis capacitive accelerometers and another with large resonant frequency reported in the literature with the modified designs that include displacement-amplifying compliant mecha- nisms (DaCMs) occupying the same footprint and under identical conditions. We show that 62% improvement in sensitivity and 34% improvement in bandwidth in the former, and 27% and 25% in the latter can be achieved. Also presented here is a dual- axis accelerometer that uses a suspension that decouples and amplifies the displacements along the two in-plane orthogonal axes. The new design was microfabricated, packaged, and tested. The device is 25-μm thick with the interfinger gap as large as 4 μm. Despite the simplicity of the microfabrication process, the measured axial sensitivity (static) of about 0.58 V/g for both the axes was achieved with a cross-axis sensitivity of less than ±2%. The measured natural frequency along the two in-plane axes was 920 Hz. Displacement amplification of 6.2 was obtained using the DaCMs in the dual-axis accelerometer. [2013-0083] Index Terms— Compliant mechanism, displacement amplifica- tion, DaCM, dual-axis micromachined accelerometer, sensitivity enhancement. I. I NTRODUCTION M ICROMACHINED accelerometers are increasingly used in many applications because of their success- ful miniaturization and cost-effective batch-fabrication. Some applications such as inertial navigation, tilt-control in space- craft, surveillance, oil exploration, and earthquake detection, etc., require high sensitivity and low noise-floor. Some appli- cations also require large bandwidth, which requires high res- onance frequency and low damping. Simultaneously achieving high sensitivity and resonance frequency is difficult because there is inherent tradeoff between the two. Mechanical ampli- fication of the displacement helps to some extent in reducing this compromise, as shown in this paper. Manuscript received March 26, 2013; revised November 15, 2013; accepted December 27, 2013. Date of publication February 7, 2014; date of current version July 29, 2014. This work was supported in part by the Indian Space Research Organization, and in part by the Naval Physical and Oceanographic Laboratory. Subject Editor A. M. Shkel. The authors are with the Department of Mechanical Engineer- ing, Indian Institute of Science, Bangalore 560012, India (e-mail: sambud@mecheng.iisc.ernet.in; suresh@mecheng.iisc.ernet.in). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JMEMS.2014.2300231 Fig. 1. A Displacement-amplifying Compliant Mechanism (DaCM) inte- grated to the proof-mass of an accelerometer. A sense-comb is attached at the output end of the DaCM whereas the input end, which hardly moves, is attached to the proof-mass. Several techniques were developed in the last two decades to address the need for high sensitivity. Some that use tun- neling current [1]–[7] or laser interferometry [8]–[10] are not suitable for lightweight and portable applications. Among the relatively simple transduction principles, capacitive [11]–[19], piezoelectric [20], [21], piezoresistive [22]–[26], and reso- nant [27]–[30] techniques are dominant. The capacitive type is reported in the literature with some of the most highly sensitive accelerometers [11]–[19]. They use either high- precision custom-made interface electronics (e.g., [19]) or very demanding micromachining processes (e.g., [11]–[14], [17], and [18]). In this paper, we present a mechanical displacement- amplifying technique that can be used to improve the sensi- tivity further, by design. A mechanical amplifier can be as simple as a lever [19], [29], [30] or as elaborate as a Displacement-amplifying Com- pliant Mechanism (DaCM) [31] shown in Fig. 1. The input of the DaCM is attached to the proof-mass. As can be seen in Fig. 1, a sense-comb is attached at the output of the DaCM where the displacement is significantly more than that at the proof-mass. The ratio of the output and input displacements of a DaCM is called its geometric advantage (GA). Since a DaCM is indeed a lever at the abstract level, their comparison is pertinent. 1057-7157 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.