Gerardo Jaramillo

Hemispherical wineglass resonators fabricated from the microcrystalline diamond

We present the development of millimeter scale 3D hemispherical shell resonators fabricated from the polycrystalline diamond, a material with low thermoelastic damping and very high stiffness. These hemispherical wineglass resonators with 1.1 mm diameter are fabricated through a combination of micro-electro discharge machining (EDM) and silicon micromachining techniques. Using piezoelectric and electrostatic excitation and optical vibration measurement, the elliptical wineglass vibration mode is determined to be at 18.321 kHz, with the two degenerate wineglass modes having a relative frequency mismatch of 0.03%. A study on the effect of the size and misalignment of the anchor and resonator’s radius variation on both the average frequency and frequency mismatch of the 2θ elliptical vibration modes is carried out. It is shown that the absolute frequency of a wineglass resonator will increase with the anchor size. It is also demonstrated that the fourth harmonic of radius variation is linearly related to the frequency mismatch. (Some figures may appear in colour only in the online journal)

MEMS Electrometer With Femtoampere Resolution for Aerosol Particulate Measurements

Electrostatic charge measurements are at the base of chemical, physical and biological experiments. In this paper, we present an electrometer based on the vibrating capacitance of a microelectromechanical systems (MEMS) resonator for the detection of small currents from ionized particles in an aerosol particle detection system. We use a porous sensing-electrode coupled to a MEMS resonating electrometer. Operating at resonance, charge is collected on the MEMS electrometer and modulated at the resonant frequency and its harmonics. Induced voltage is read with a low-leakage very high-input impedance feedback amplifier. Because of the specific readout technique, a switched-reset is used to prevent charge saturation. Sensitivity improvements are achieved by modifying the low noise-readout amplifier by reducing input-referred noise and parasitic capacitance. The electrometer achieves a noise floor <;1 fA produced by 10 nm diameter particles within an airflow of 1.0 L/min. At this flow rate, the minimum detectable current (1 fA) corresponds to a minimum measureable particle density of 400 cm-3. The MEMS electrometer is compared with and calibrated against commercial electrometer and a particle counter, respectively.

Magnetic Scanometric DNA Microarray Detection of Methyl Tertiary Butyl Ether Degrading Bacteria for Environmental Monitoring

A magnetoresistive biosensing platform based on a single magnetic tunnel junction (MTJ) scanning probe and DNA microarrays labeled with magnetic particles has been developed to provide an inexpensive, sensitive and reliable detection of DNA. The biosensing platform was demonstrated on a DNA microarray assay for quantifying bacteria capable of degrading methyl tertiary butyl ether (MTBE), where concentrations as low as 10 pM were detectable. Synthetic probe bacterial DNA was immobilized on a microarray glass slide surface, hybridized with the 48 base pair long biotinylated target DNA and subsequently incubated with streptavidin-coated 2.8 μm diameter magnetic particles. The biosensing platform then makes use of a micron-sized MTJ sensor that was raster scanned across a 3 mm by 5 mm glass slide area to capture the stray magnetic field from the tagged DNA and extract two dimensional magnetic field images of the microarray. The magnetic field output is then averaged over each 100 μm diameter DNA array spot to extract the magnetic spot intensity, analogous to the fluorescence spot intensity used in conventional optical scanners. The magnetic scanning result is compared with results from a commercial laser scanner and particle coverage optical counting to demonstrate the dynamic range and linear sensitivity of the biosensing platform as a potentially inexpensive, sensitive and portable alternative for DNA microarray detection for field applications.

Towards picoTesla Magnetic Field Detection Using a GMR-MEMS Hybrid Device

We are developing a novel MEMS-magnetoresistive hybrid device aimed at ultra low magnetic field detection. The hybrid device combines magnetoresistive (MR) sensors and AlN based piezoelectric MEMS resonators. The MR sensor can achieve highly sensitive magnetic field detection but suffers from high magnetic and electrical 1/f noise, limiting its applicability for dc and low-frequency field detection. We overcome this problem by using two piezoelectric cantilevers with integrated magnetic flux concentrators (MFC) to mechanically modulate the external magnetic fields into the high frequency region where the 1/f noise in the MR device vanishes. In this paper we report our fabrication approach and preliminary characterization of the hybrid device.

Pyroelectric aluminum nitride micro electromechanical systems infrared sensor with wavelength-selective infrared absorber

This paper describes a micro electromechanical systems type wavelength-selective pyroelectric sensor, with highly c-axis oriented Aluminum nitride film as the pyroelectric material. Wavelength-selective infrared absorption is realized via periodic structures of holes patterned into the top metal electrode that also collects pyroelectric charge signal. The periodic hole array results in optical absorption resonances whose wavelength is determined by the hole pitch, demonstrated experimentally using a Fourier transform infrared spectrometer and numerically calculated using the finite difference time domain method. A significant difference in infrared absorption between patterned and unpatterned detectors is demonstrated through optical experiments comparing the pyroelectric responses.

Scanning Magnetoresistance Microscopy for Imaging Magnetically Labeled DNA Microarrays

We demonstrate the use of a magnetic tunnel junction (MTJ) sensor as a probe for non-contact scanning microscopy of magnetically labeled DNA microarrays. Induced magnetic stray fields from 2.8 mum diameter magnetic particles are detected using the MTJ sensor, while two dimensional scanning generates the magnetic map of the DNA microarray with a spatial resolution of 1 mum over a large scan area exceeding 1 cm2. Current particle-sensor spacing of ~20 mum results in a detection resolution of ~30 magnetic particles within each 100 mum diameter DNA spot. Our results highlight the use of scanning magnetoresistive microscopy as a convenient and powerful technique for the accurate detection and identification of biomolecules tagged with magnetic particles.

Hybrid GMR Sensor Detecting 950 pT/sqrt(Hz) at 1 Hz and Room Temperature

Advances in the magnetic sensing technology have been driven by the increasing demand for the capability of measuring ultrasensitive magnetic fields. Among other emerging applications, the detection of magnetic fields in the picotesla range is crucial for biomedical applications. In this work Picosense reports a millimeter-scale, low-power hybrid magnetoresistive-piezoelectric magnetometer with subnanotesla sensitivity at low frequency. Through an innovative noise-cancelation mechanism, the 1/f noise in the MR sensors is surpassed by the mechanical modulation of the external magnetic fields in the high frequency regime. A modulation efficiency of 13% was obtained enabling a final device’s sensitivity of ~950 pT/Hz1/2 at 1 Hz. This hybrid device proved to be capable of measuring biomagnetic signals generated in the heart in an unshielded environment. This result paves the way for the development of a portable, contactless, low-cost and low-power magnetocardiography device.

Ferrite Scanning Microscope Based on Magnetic Tunnel Junction Sensor

We have developed a scanning magnetic microscope (SMM) based on a magnetic tunneling junction (MTJ) magnetoresistive (MR) sensor. The microscope is based on commercially available components employing two sets of scanning stages and a MTJ sensor. Spatial resolution and noise sensitivity were investigated using two MTJ sensors, one having high spatial resolution and the other low noise but coarser spatial resolution. We present measurements of magnetic field images from ferrite concentration calibration standards and a stainless steel welded specimen both imaged using a magnetoresistive scanning microscope. A sensitivity of ~ 10 μT/FN was obtained from standards with defined ferrite numbers (FN). This microscope represents a new powerful tool for the characterization and investigations of delta ferrite concentrations in stainless steel welded samples.

A MEMS based electrometer with a low-noise switched reset amplifier for charge measurement

Electrostatic charge measurements are at the base of chemical, physical and biological experiments. In this work the authors present an electrometer based on the vibrating capacitance of a microelectromechanical (MEMS) micromachined resonator. We present improvements on the low-noise readout amplifier by reducing input-referred voltage noise and parasitic capacitances. An amplifier has been designed to have a noise corner frequency well below the devices operating frequency fn. The electrometer geometry allows for charge output signal measurements at 2fn minimizing feedthrough of driving signals. The sensor consists of a set of comb-finger capacitors placed on each side of a moving mass for push-pull driving. Operating at resonance, charge collected on the moving electrode is modulated and the induced voltage is read with a low-leakage very high-input impedance feedback amplifier. Due to the specific readout technique, a switched-reset is used to prevent charge saturation. Reduction of parasitic capacitance and increase in resolution is achieved through the careful selection and placement of discrete electronic components alongside the silicon MEMS chip.

Integration of MEMS Actuators with Magnetic Tunnel Junction Sensors

We are developing techniques to integrate magnetic tunnel junction (MTJ) sensors with MEMS actuators for magnetic scanning-probe microscopy applications. In this application, the MTJ sensor is raster-scanned over a specimen and spatial variations in the magnetic field are recorded. We have developed a fabrication process where the MTJ sensor is fabricated first on the surface of an SOI wafer. Subsequently, MEMS actuators are fabricated in a two step deep reactive ion etching process. We have carried out electromechanical testing of the actuator voltage-to-position and frequency response. MEMS actuators are uniquely suited to achieve both precise, micron-scale control of the average sample-to-sensor separation and to AC modulate the separation and MTJ signal at a very high frequency (>10 kHz).