Fast on-wafer electrical, mechanical, and electromechanical characterization of piezoresistive cantilever force sensors

Validation of a technological process requires an intensive characterization of the performance of the resulting devices, circuits, or systems. The technology for the fabrication of micro and nanoelectromechanical systems (MEMS and NEMS) is evolving rapidly, with new kind of device concepts for applications like sensing or harvesting are being proposed and demonstrated. However, the characterization tools and methods for these new devices are still not fully developed. Here, we present an on-wafer, highly precise, and rapid characterization method to measure the mechanical, electrical, and electromechanical properties of piezoresistive cantilevers. The setup is based on a combination of probe-card and atomic force microscopy technology, it allows accessing many devices across a wafer and it can be applied to a broad range of MEMS and NEMS. Using this setup we have characterized the performance of multiple submicron thick piezoresistive cantilever force sensors. For the best design we have obtained a force sensitivity ℜ_F = 158μV/nN, a noise of 5.8 μV (1 Hz–1 kHz) and a minimum detectable force of 37 pN with a relative standard deviation of σ_r ≈ 8%. This small value of σr, together with a high fabrication yield >95%, validates our fabrication technology. These devices are intended to be used as bio-molecular detectors for the measurement of intermolecular forces between ligand and receptor molecule pairs

Geometrical Considerations for the Design of Liquid-phase Biochemical Sensors Using a Cantilever\u27s Fundamental In-plane Mode

The influence of the beam geometry on the quality factor and resonance frequency of resonant silicon cantilever beams vibrating in their fundamental in-plane flexural mode in water has been investigated. Compared to cantilevers vibrating in their first out-of-plane flexural mode, utilizing the in-plane mode results in reduced damping and reduced mass loading by the surrounding fluid. Quality factors as high as 86 have been measured in water for cantilevers with a 20 μm thick silicon layer. Based on the experimental data, design guidelines are established for beam dimensions that ensure maximal Q-factors and minimal mass loading by the surrounding fluid, thus improving the limit-of-detection of mass-sensitive biochemical sensors. Elementary theory is also presented to help explain the observed trends. Additional discussion focuses on the tradeoffs that exist in designing liquid-phase biochemical sensors using in-plane cantilevers

A Comparative Study Between a Micromechanical Cantilever Resonator and MEMS-based Passives for Band-pass Filtering Application

Over the past few years, significant growth has been observed in using MEMS based passive components in the RF microelectronics domain, especially in transceiver components. This is due to some excellent properties of the MEMS devices like low loss, excellent isolation etc. in the microwave frequency domain where the on-chip passives normally tend to become leakier and degrades the transceiver performance. This paper presents a comparative analysis between MEMS-resonator based and MEMS-passives based band-pass filter configurations for RF applications, along with their design, simulation, fabrication and characterization. The filters were designed to have a center frequency of 455 kHz, meant for use as the intermediate frequency (IF) filter in superheterodyne receivers. The filter structures have been fabricated in PolyMUMPs process, a three-polysilicon layer surface micromachining process.Comment: 6 pages, 15 figure

Resonant Characteristics of Rectangular Hammerhead Microcantilevers Vibrating Laterally in Viscous Liquid Media

The resonant characteristics of laterally vibrating rectangular hammerhead microcantilevers in viscous liquid media are investigated. The rectangular hammerhead microcantilever is modeled as an Euler-Bernoulli beam (stem) and a rigid body (head). A modified semi-analytical expression for the hydrodynamic function in terms of the Reynolds number, Re, and aspect ratio, h/b, is proposed to rapidly evaluate the sensing characteristics. Using this expression, the resonance frequency, quality factor and normalized surface mass sensitivity are investigated as a function of the dimensions of the microcantilever and liquid properties. Guidelines for design of hammerhead microcantilever geometry are proposed to achieve efficient sensing platforms for liquid-phase operation. The improvement in the sensing area and characteristics are expected to yield higher sensitivity of detection and improved signal-to-noise ratio in liquid-phase chemical sensing applications

Materials selection and design of microelectrothermal bimaterial actuators

A common form of MEMS actuator is a thermally actuated bimaterial, which is easy to fabricate by surface micromachining and permits out of plane actuation, which is otherwise difficult to achieve. This paper presents an analytical framework for the design of such microelectrothermal bimaterial actuators. Mechanics relationships for a cantilever bimaterial strip subjected to a uniform temperature were applied to obtain expressions for performance metrics for the actuator, i.e., maximum work/volume, blocked (force) moment, and free-end (displacement) slope. Results from finite-element analysis and closed form relations agree well to within 1%. The optimal performance for a given pair of materials and the corresponding thickness ratio were determined. Contours of equal performance corresponding to commonly used substrates (e.g., Si, SiO2) were plotted in the domain of governing material properties (thermal expansion coefficient and Young's modulus) to identify candidate materials for further development. These results and the accompanying methodology provide a rational basis for comparing the suitability of "standard" materials for microelectrothermal actuators, as well as identifying materials that might be suitable for further research

Cantilever-based Resonant Microsensors with Integrated Temperature Modulation for Transient Chemical Analysis

This work introduces a resonant cantilever platform with integrated temperature modulation for real-time chemical sensing. Embedded heaters allow for rapid thermal cycling of individual sensors, thereby enabling real-time transient signal analysis without the need for a microfluidic setup to switch between analyte and reference gases. Compared to traditional mass-sensitive microsensors operating in steady state, the on-chip generation of signal transients provides additional information for analyte discrimination

Electrostatically Tunable Meta-Atoms Integrated With In Situ Fabricated MEMS Cantilever Beam Arrays

Two concentric split ring resonators (SRRs) or meta-atoms designed to have a resonant frequency of 14 GHz are integrated with microelectromechanical systems cantilever arrays to enable electrostatic tuning of the resonant frequency. The entire structure was fabricated monolithically to improve scalability and minimize losses from externally wire-bonded components. A cantilever array was fabricated in the gap of both the inner and outer SRRs and consisted of five evenly spaced beams with lengths ranging from 300 to 400 μm. The cantilevers pulled in between 15 and 24 V depending on the beam geometry. Each pulled-in beam increased the SRR gap capacitance resulting in an overall 1-GHz shift of the measured meta-atom resonant frequency

SRRs Embedded with MEMS Cantilevers to Enable Electrostatic Tuning of the Resonant Frequency

A microelectromechanical systems (MEMS) cantilever array was monolithically fabricated in the gap region of a split ring resonator (SRR) to enable electrostatic tuning of the resonant frequency. The design consisted of two concentric SRRs each with a set of cantilevers extending across the split region. The cantilever array consisted of five beams that varied in length from 300 to 400 μm, with each beam adding about 2 pF to the capacitance as it actuated. The entire structure was fabricated monolithically to reduce its size and minimize losses from externally wire bonded components. The beams actuate one at a time, longest to shortest with an applied voltage ranging from 30–60 V. The MEMS embedded SRRs displayed dual resonant frequencies at 7.3 and 14.2 GHz or 8.4 and 13.5 GHz depending on the design details. As the beams on the inner SRR actuated the 14.2 GHz resonance displayed tuning, while the cantilevers on the outer SRR tuned the 8.4 GHz resonance. The 14.2 GHz resonant frequency shifts 1.6 GHz to 12.6 GHz as all the cantilevers pulled-in. Only the first two beams on the outer cantilever array pulled-in, tuning the resonant frequency 0.4 GHz from 8.4 to 8.0 GHz