Piezoresistive Detection Research Articles

A Bistable Microelectromechanical System Actuated by Spin‐Crossover Molecules

AbstractWe report on a bistable MEMS device actuated by spin‐crossover molecules. The device consists of a freestanding silicon microcantilever with an integrated piezoresistive detection system, which was coated with a 140 nm thick film of the [Fe(HB(tz)3)2] (tz=1,2,4‐triazol‐1‐yl) molecular spin‐crossover complex. Switching from the low‐spin to the high‐spin state of the ferrous ions at 338 K led to a reversible upward bending of the cantilever in agreement with the change in the lattice parameters of the complex. The strong mechanical coupling was also evidenced by the decrease of approximately 66 Hz in the resonance frequency in the high‐spin state as well as by the drop in the quality factor around the spin transition.

A Bistable Microelectromechanical System Actuated by Spin-Crossover Molecules.

We report on a bistable MEMS device actuated by spin-crossover molecules. The device consists of a freestanding silicon microcantilever with an integrated piezoresistive detection system, which was coated with a 140 nm thick film of the [Fe(HB(tz)3 )2 ] (tz=1,2,4-triazol-1-yl) molecular spin-crossover complex. Switching from the low-spin to the high-spin state of the ferrous ions at 338 K led to a reversible upward bending of the cantilever in agreement with the change in the lattice parameters of the complex. The strong mechanical coupling was also evidenced by the decrease of approximately 66 Hz in the resonance frequency in the high-spin state as well as by the drop in the quality factor around the spin transition.

Magnetoelectric versus thermal actuation characteristics of shear force AFM probes with piezoresistive detection

In this paper the authors compare methods used for piezoresistive microcantilevers actuation for the atomic force microscopy (AFM) imaging in the dynamic shear force mode. The piezoresistive detection is an attractive technique comparing the optical beam detection of deflection. The principal advantage is that no external alignment of optical source and detector are needed. When the microcantilever is deflected, the stress is transferred into a change of resistivity of piezoresistors. The integration of piezoresistive read-out provides a promising solution in realizing a compact non-contact AFM.Resolution of piezoresistive read-out is limited by three main noise sources: Johnson, 1/f and thermomechanical noise. In the dynamic shear force mode measurement the method used for cantilever actuation will also affect the recorded noise in the piezoresistive detection circuit. This is the result of a crosstalk between an aluminium path (current loop used for actuation) and piezoresistors located near the base of the beam.In this paper authors described an elaborated in ITE (Institute of Electron Technology) technology of fabrication cantilevers with piezoresistive detection of deflection and compared efficiency of two methods used for cantilever actuation.

Development of Ultrasensitive Terahertz ESR Spectroscopy for Metalloprotein Using a Microcantilever

In this article, we report a novel method for ultrasensitive high-frequency electron spin resonance (HFESR) using a microcantilever. With this method, a field-gradient force exerting on a sample-holding cantilever is detected as cantilever displacement. A unique feature of this method is that a very tiny sample (~1 µg) is sufficient for HFESR measurement in the terahertz region. Thus, the application of this method to metalloprotein is expected to be of particular interest in the future. In this study, we developed two types of HFESR techniques: one for fiber-optic detection and the other for piezoresistive detection. We applied these techniques to multi-frequency HFESR measurements of metal-containing porphyrin compounds as a model metalloprotein substance and evaluated the sensitivity and feasibility of each technique.

Microelectromechanical systems integrating molecular spin crossover actuators

Silicon MEMS cantilevers coated with a 200 nm thin layer of the molecular spin crossover complex [Fe(H2B(pz)2)2(phen)] (H2B(pz)2 = dihydrobis(pyrazolyl)borate and phen = 1,10-phenantroline) were actuated using an external magnetic field and their resonance frequency was tracked by means of integrated piezoresistive detection. The light-induced spin-state switching of the molecules from the ground low spin to the metastable high spin state at 10 K led to a well-reproducible shift of the cantilever's resonance frequency (Δfr = −0.52 Hz). Control experiments at different temperatures using coated as well as uncoated devices along with simple calculations support the assignment of this effect to the spin transition. This latter translates into changes in mechanical behavior of the cantilever due to the strong spin-state/lattice coupling. A guideline for the optimization of device parameters is proposed so as to efficiently harness molecular scale movements for large-scale mechanical work, thus paving the road for nanoelectromechanical systems (NEMS) actuators based on molecular materials.

Sensitivity Analysis of Rectangular Microcantilever Structure with Piezoresistive Detection Technique Using Coventorware FEA

Micro Electro Mechanical Systems (MEMS) based microcantilever is a micromachined device similar to the miniaturized version of a diver's board, longer as compared to width, and has a thickness much smaller than its length or width. The merits of MEMS microcantilever sensors are its high sensitivity, design simplicity, portability and high speed. In this paper, a microcantilever sensor is designed to meet the requirements of a biosensor that detects tuberculosis. The addition of mass on the microcantilever surface makes it to bend and its stressed elements deform.The deflection underwent by microcantilever is detected by piezoresistive detection mechanism. The behavior of piezoresistive microcantilever structure is investigated using various beam materials and geometric dimensions. The advantage of incorporating SCR (Stress Concentrated Region) on the piezoresistive microcantilever is studied and the optimal position of placing the piezoresistor on the microcantilever beam is investigated using load analysis and corresponding stress distribution results. CoventorWare® is used to do the analysis of micromachined cantilever. The results show that sensitivity increases with increase in length and incorporation of SCR but decreases with increase in thickness.

In-Plane and Out-of-Plane MEMS Gyroscopes Based on Piezoresistive NEMS Detection

This paper presents a new design and a complete characterization of amplitude-modulation gyroscopes based on piezoresistive nanogauges. The working principle and optimization criteria of in-plane and out-of-plane devices relying on double frame decoupling and levered sense mode are discussed in light of sensitivity and resolution theoretical predictions. The architecture of driving and sensing electronics is also presented. The reduced thermo-mechanical damping with respect to capacitive configurations, and the inherently high output signal leads to white noise performance in the mdps/ $\surd $ Hz range within an area smaller than 0.35 mm $^{\mathrm { {2}}}$ , at pressures in the millibar range. Sub-5-ppm linearity errors within 1000 dps are also demonstrated. [2015-0064]

Experimental Investigations on New Characterization Method for Giant Piezoresistance Effect and Silicon Nanowire Piezoresistive Detection

This paper presents a novel and effective characterization method for giant piezoresistive properties of silicon nanowires by using the reference structures. This contrast detection approach investigates the influences of quantum size effect and surface defects effect on piezoresistive coefficients of silicon nanowires by direct comparison of the resistivity change ratio of silicon wires with nanoscale-to-microscale width under the same applied stress conditions. The characterization experiments based on four-point bending tensile test demonstrate that piezoresistive coefficient of small nanowidth silicon nanowire can be significantly increased to about five times higher levels than that of bulk silicon under the same impurity concentration, which indicates that the silicon nanowire can have giant piezoresistive effect. On the other hand, to solve the problem on nanowires pick-up, we proposed a nanowire piezoresistive detection approach, whose validity is confirmed by the dynamic LDV resonance test. Meanwhile, to investigate the influence of undercut arising from the wet chemical release process of the suspended silicon nanowire, a three-dimensional finite element simulation is also carried out for the fundamental resonant frequency using ANSYS software. The numerical and experimental results show that our piezoresistive detection is accurate and effective and the undercut should be carefully considered in the design of the high frequency resonator and mixer. The findings of this paper provide some useful references for the piezoresistive effect measurement and the piezoresistive pick-up in nanoelectromechanical system.

A Novel Dog-Bone Oscillating AFM Probe with Thermal Actuation and Piezoresistive Detection

In order to effectively increase the resonance frequency and the quality factor of atomic force microscope (AFM) probes, a novel oscillating probe based on a dog-bone shaped MEMS resonator was conceived, designed, fabricated and evaluated. The novel probe with 400 μm in length, 100 μm in width and 5 μm in thickness was enabled to feature MHz resonance frequencies with integrated thermal actuation and piezoresistive detection. Standard silicon micromachining was employed. Both electrical and optical measurements were carried out in air. The resonance frequency and the quality factor of the novel probe were measured to be 5.4 MHz and 4000 respectively, which are much higher than those (about several hundreds of kHz) of commonly used cantilever probes. The probe was mounted onto a commercial AFM set-up through a dedicated probe-holder and circuit board. Topographic images of patterned resist samples were obtained. It is expected that the resonance frequency and the measurement bandwidth of such probes will be further increased by a proper downscaling, thus leading to a significant increase in the scanning speed capability of AFM instruments.

Scanning probes in nanostructure fabrication

Scanning probes have enabled modern nanoscience and are still the backbone of today's nanotechnology. Within the technological development of AFM systems, the cantilever evolved from a simple passive deflection element to a complex microelectromechanical system through integration of functional groups, such as piezoresistive detection sensors and bimaterial based actuators. Herein, the authors show actual trends and developments of miniaturization efforts of both types of cantilevers, passive and active. The results go toward the reduction of dimensions. For example, the authors have fabricated passive cantilever with a width of 4 μm, a length of 6 μm and thickness of 50–100 nm, showing one order of magnitude lower noise levels. By using active cantilevers, direct patterning on calixarene is demonstrated employing a direct, development-less phenomena triggered by tip emitted low energy (<50 eV) electrons. The scanning probes are not only applied for lithography, but also for imaging and probing of the surface before and immediately after scanning probe patterning. In summary, piezoresistive probes are comparable to passive probes using optical read-out. They are able to routinely obtain atomic step resolution at a low thermal noise floor. The active cantilever technology offers a compact, integrated system suited for integration into a table-top scanning probe nanolithography tool.

Electrothermally driven high-frequency piezoresistive SiC cantilevers for dynamic atomic force microscopy

Cantilevers with resonance frequency ranging from 1 MHz to 100 MHz have been developed for dynamic atomic force microscopy. These sensors are fabricated from 3C-SiC epilayers grown on Si(100) substrates by low pressure chemical vapor deposition. They use an on-chip method both for driving and sensing the displacement of the cantilever. A first gold metallic loop deposited on top of the cantilever is used to drive its oscillation by electrothermal actuation. The sensing of this oscillation is performed by monitoring the resistance of a second Au loop. This metallic piezoresistive detection method has distinct advantages relative to more common semiconductor-based schemes. The optimization, design, fabrication, and characteristics of these cantilevers are discussed.

A Flowmeter with Piezoresistive Metal Layer Deposited with Focused-Ion-Beam System

In this paper, we fabricated and evaluated a flowmeter with a sub-micron sized piezoresistive layer for the measurement in the small area. For the small area detection, the sensing material should be reduced as well as sensor body. We use the FIB system to reduce the size of the sensing material and obtain the sub-micron sized line width. The device is fabricated with the standard MEMS process, and the platinum layer is selected as the piezoresistive material considering the electrical conductivity. The 0∼4m/s air flows are applied to the flowmeter and the experimental results shows the negative sensitivity output with -3.22E−5/ms−1. This negative value is due to the additional materials like carbon and gallium. The various experiments including stability and repeatability are performed, and the repeated operation shows stable output signals with less than 9.6% variation. Through those experiment results, the FIB assisted platinum layer is suitable for the piezoresistive detection and a flowmeter can be applied to measurement of flow rate in the small area.

3D Magnetic Field Sensor Concept for Use in Inertial Measurement Units (IMUs)

We report on the design, fabrication, and characterization of a microfabricated 3D magnetic field sensor that is suitable for co-integration with inertial sensors to form single-chip inertial measurement units. In contrast to classical resonant MEMS magnetometers, which are based on Lorentz force measurement, our sensor uses permanent magnetic materials and piezoresistive detection with silicon strain gauges of nanometric section, leading to low power consumption and high sensitivity for small sensor size. Thin multilayers of CoFe and PtMn as ferro- and antiferromagnetic materials are integrated within the MEMS fabrication process. Sensitivities of 1.09 V/T for x- and y- components of the magnetic field and 0.124 V/T for z- component of the magnetic field were measured, respectively. To be sensitive to magnetic fields along all three spatial directions, two permanent magnetization directions on the same die are required. Implementation of the two magnetization directions was validated by a measured correlation of 99.7% between x- and y- sensitivity axes. Power consumption of the 3D sensor is for polarization with a 100 μA dc current. With resolutions of 100 nT/√Hz for x- and y-component of the magnetic field and 350 nT/√Hz for z- component, the sensor is suitable for precise measurement of earth magnetic field.

Junctionless Silicon Nanowire Resonator

The development of nanoelectromechanical systems (NEMS) is likely to open up a broad spectrum of applications in science and technology. In this paper, we demonstrate a novel double-transduction principle for silicon nanowire resonators, which exploits the depletion charge modulation in a junctionless field effect transistor body and the piezoresistive modulation. A mechanical resonance at the very high frequency of 100 MHz is detected in the drain current of the highly doped silicon wire with a cross-section down to ~ 30 nm. We show that the depletion charge modulation provides a ~ 35 dB increase in output signal-to-noise compared to the second-order piezoresistive detection, which can be separately investigated within the same device. The proposed junctionless resonator stands, therefore, as a unique and valuable tool for comparing the field effect and the piezoresistive modulation efficiency in the same structure, depending on size and doping. The experimental frequency stability of 10 ppm translates into an estimated mass detection noise floor of ~ 60 kDa at a few seconds integration time in high vacuum and at room temperature. Integrated with conventional semiconductor technology, this device offers new opportunities for NEMS-based sensor and signal processing systems hybridized with CMOS circuitry on a single chip.

Contact Mode MEMS Position Sensors with Piezoresistive Detection

Abstract Measuring of linear position with contact MEMS sensors is a promising option for achieving sub-nm resolution, as demanded by micro-/nanotechnology community [1] . The position of specific point of interest can be calculated by bending detection of cantilevers or more complex MEMS flexures via different techniques: optical, capacitive, piezoelectric, etc. Prototyping of strain sensing devices with sidewall piezoresistors has been preferred in the present study due to multiple advantages, like: very few restrictions in flexures design, very high signal sensitivity and linearity, temperature and noise stability and CMOS compatibility. Comprehensive results obtained at characterization of contact MEMS position sensors, comprising two rigid members, monolithic flexures with various layouts and electrically identical piezoresistors for strain detection, are presented. Design approach for setting the sensitivity in the range from 20 μV/μm.V to 2 mV/μm.V has been demonstrated. Recently achieved results report extremely high temperature immunity of the sensor signal.

Differentially Piezoresistive Sensing for CMOS-MEMS Resonators

A foundry-oriented capacitively driven CMOS-MEMS resonator using differentially piezoresistive sensing is successfully demonstrated to enable effective feedthrough cancellation with more than 20-dB feedthrough floor reduction as compared to its capacitive readout. The resonator is mainly formed by high-Q SiO2 structure utilizing metal wet etching and XeF2 release processes, while the polysilicon layer (originally CMOS gate poly material) embedded inside the resonator structure serves as a piezoresistor for vibratory detection. In addition, such a composite structure enabling electrical isolation realizes decoupling of the capacitive and piezoresistive transductions, allowing the selection (or switching) of the preferred readout scheme using the same resonator device. The proposed resonator consists of only one single capacitor for driving and a simple beam structure for both vibration and detection, therefore greatly simplifying the device design and facilitating future CMOS-MEMS implementation. This paper achieves resonator , more than 28-dB signal-to-feedthrough ratio, and two-times smaller motional impedance than that of the single-ended piezoresistive detection using the same device and driving condition. Furthermore, the piezoresistive operation offers a simple temperature compensation scheme for CMOS-MEMS resonators via the adjustment of the dc current through the piezoresistor, therefore showing 1.4-times improvement on thermal stability as compared to their capacitive readout.

Enhancing sensitivity in a piezoresistive cantilever-based label-free DNA detection assay using ssPNA sensor probes

In this work, a strategy for enhancing sensitivity in a label-free DNA detection assay, where the basic operational principle involves detection of the net surface stress induced bending motion of a piezoresistive microcantilever, upon target-binding, has been presented. A microcantilever array that allows experiments using sensor-reference configuration has been employed, where the cantilevers have been functionalized by inkjet printing technology, using short nucleic acid sequences of similar length (here, 12-mer), on both the sensor and the reference cantilevers. It is shown that application of the single stranded peptide nucleic acids (PNA), having non-ionic peptidic backbone, as the sensor probes improves the assay sensitivity about twenty times, even to the level of single base mismatch discrimination, compared to the DNA counterparts. We propose that the significantly improved performance of the PNA-based assay could be due to the orientational advantage of PNA probes as offered when a self-assembled ordered PNA structure is formed. Since the piezoresistive cantilever based method offers a practical means for target detection by rapid monitoring of the recognition events in fluid in real time, and importantly, since PNA is nuclease-resistant, this step of advancement may motivate future endeavours for detection of nucleic acid sequences in complex body fluid mimics.

Observation of Nonlinear Dissipation in Piezoresistive Diamond Nanomechanical Resonators by Heterodyne Down-Mixing

We report the observation of nonlinear dissipation in diamond nanomechanical resonators measured by an ultrasensitive heterodyne down-mixing piezoresistive detection technique. The combination of a hybrid structure as well as symmetry breaking clamps enables sensitive piezoresistive detection of multiple orthogonal modes in a diamond resonator over a wide frequency and temperature range. Using this detection method, we observe the transition from purely linear dissipation at room temperature to strongly nonlinear dissipation at cryogenic temperatures. At high drive powers and below liquid nitrogen temperatures, the resonant structure dynamics follows the Pol-Duffing equation of motion. Instead of using the broadening of the full width at half-maximum, we propose a nonlinear dissipation backbone curve as a method to characterize the strength of nonlinear dissipation in devices with a nonlinear spring constant.

Cantilever Resonator With Integrated Actuation and Sensing Fabricated Using a Single Step Lithography

Micro- and nano-mechanical resonators have been proposed for a variety of applications ranging from mass sensing to signal processing. Often their actuation and/or detection involve external subsystems that are much larger than the resonator itself. We have designed a simple microcantilever resonator with integrated sensor and actuator, facilitating the integration of large arrays of resonators. This unique design can be manufactured with a low-cost fabrication process, involving just a single step of lithography. The bilayer cantilever of gold and silicon dioxide is used as piezoresistive sensor as well as thermal bimorph actuator. The ac current used for actuation and the dc current used for piezoresistive detection are separated in the frequency-domain using a bias-tee circuit configuration. The resonant response is measured by detecting the second harmonic of the actuation current using a lock-in amplifier.

MEMS piezoresistive ring resonator for AFM imaging with pico-Newton force resolution

A new concept of atomic force microscope (AFM) oscillating probes using electrostatic excitation and piezoresistive detection is presented. The probe is characterized by electrical methods in vacuum and by mechanical methods in air. A frequency-mixing measurement technique is developed to reduce the parasitic signal floor. The probe resonance frequencies are in the 1 MHz range and the quality factor is measured about 53 000 in vacuum and 3000 in air. The ring probe is mounted onto a commercial AFM set-up and topographic images of patterned sample surfaces are obtained. The force resolution deduced from the measurements is about 10 pN Hz−0.5.