N. Scott Barker

New Detection Modality for Label-Free Quantification of DNA in Biological Samples via Superparamagnetic Bead Aggregation

Combining DNA and superparamagnetic beads in a rotating magnetic field produces multiparticle aggregates that are visually striking, enabling label-free optical detection and quantification of DNA at levels in the picogram per microliter range. DNA in biological samples can be quantified directly by simple analysis of optical images of microfluidic wells placed on a magnetic stirrer without prior DNA purification. Aggregation results from DNA/bead interactions driven either by the presence of a chaotrope (a nonspecific trigger for aggregation) or by hybridization with oligonucleotides on functionalized beads (sequence-specific). This paper demonstrates quantification of DNA with sensitivity comparable to that of the best currently available fluorometric assays. The robustness and sensitivity of the method enable a wide range of applications, illustrated here by counting eukaryotic cells. Using widely available and inexpensive benchtop hardware, the approach provides a highly accessible low-tech microscale alternative to more expensive DNA detection and cell counting techniques.

A 60-GHz 2-bit Switched-Line Phase Shifter Using SP4T RF-MEMS Switches

This paper presents a V -band 2-bit switched-line phase shifter using dc-contact single-pole four-throw (SP4T) RF microelectromechanical systems (RF-MEMS) switches for 60-GHz applications. The design and measurements of the SP4T RF-MEMS switches and the phase shifter are presented. The phase shifter demonstrates an average insertion loss of 2.5 dB in the 55-65-GHz band with a return loss better than 12 dB for each state. The phase error for each state of the switched-line phase shifter is less than 1° at 60 GHz.

Realization of low-stress Au cantilever beams

A significant challenge in the fabrication of thin-film (<1 µm) Au MEMS devices is maintaining planarity after removal of the sacrificial layer. Out-of-plane deformations are driven by residual stress gradients in the Au films. It was found that the baking time and temperature of the sacrificial photoresist layer, as well as the thermal history once the Au was deposited, combined to determine the stress gradient within the Au film. In this technical note we provide the complete details of the optimized procedures to fabricate planar thin-film Au devices with unattached ends that are characterized by low residual stresses.

A 3-D micromachined W-band cavity-backed patch antenna array with integrated rectacoax transition to waveguide

A 2×2 array of W-band cavity-backed patch antennas with integrated rectacoaxial feed and transition to WR-10 waveguide is presented in this paper. The array and its components are fabricated using a sequential surface micromachining technique. Each antenna has a simulated 4.1% 10-dB return-loss bandwidth about 94.5 GHz, a radiation efficiency of 95%, and a gain of 8.3 dB at broadside with a 76 degree 3-dB beamwidth. The gain of the entire array is 14.3 dB. To facilitate system integration and measurement, an integrated rectacoax-waveguide transition is included, with a simulated insertion loss of −0.1 dB. Measured return-loss shows good correlation to simulation, with a 10-dB return loss bandwidth of 4.6 GHz (4.9%), and a broadside gain of 10 dB at 95.9 GHz is also measured.

SU-8 micromachining of millimeter and submillimeter waveguide circuits

Micromachined WR 3.4 waveguide circuits are fabricated using a SU-8 micromachining process. In order to demonstrate the viability and repeatability of this process both straight waveguide sections and cylindrical cavity resonators are fabricated and measured. The SU-8 waveguide compares reasonably well to a standard WR 3.4 waveguide section. The measured cavity resonators demonstrate quality factors of 1900 and 2200 at a resonant frequency of 308 GHz.

A 1.1 THz micromachined on-wafer probe

This paper presents a micromachined probe for on-wafer measurements of circuits in the WR-1.0 waveguide band (0.75 - 1.1 THz). The probe shows a measured insertion loss of less than 7 dB and return loss of greater than 15 dB over most of the band. These are the first reported on-wafer measurements above 1 THz.

Improved Micromachined Terahertz On-Wafer Probe Using Integrated Strain Sensor

This paper introduces an improved method for monitoring and controlling the contact condition of terahertz on-wafer probes to enhance the measurement repeatability as well as probe lifetime. This method enables accurate contact force and contact angle measurements without modification to the standard probe station. Both probe contact force and contact angle are crucial for RF measurement repeatability. Repeatable probe contact force can be achieved by properly monitoring and controlling the strain generated at designated positions on the terahertz probe due to probe deformation induced by contacting the test substrate. Contact angle can be measured by asymmetrical strain on symmetrical positions of the probe when the probe is contacting the test substrate with angular misalignment. In this work a WR-1.5 (500 GHz-750 GHz) probe with integrated strain sensor is developed and tested. Mechanical tests show that the integrated sensors have a contact force resolution of 0.2 mN and a contact angle resolution of 0.05° about the center. RF tests show that repeatable measurements can be achieved with 3 mN contact force after adjusting probe contact angle using the integrated sensors, as compared to a previously reported value of 15 mN.

9.2: Fabrication techniques for a THz EIK

To produce an EIK working at THz frequencies, departure from traditional fabrication techniques is required. This paper describes the investigation and results of various fabrication techniques and their suitability for application in a VED.

A cryogenic broadband DC contact RF MEMS switch

A dielectric free DC contact RF microelectromechanical systems (MEMS) switch is designed and tested under room temperature and cryogenic temperature. The switch demonstrates a 1 Ω contact resistance and 2 fF up-state capacitance, and thus has an insertion-loss less than 0.4 dB up to 50 GHz and less than 0.9 dB up to 75 GHz at room temperature. The isolation is better than 24 dB up to 50 GHz and 18 dB up to 75 GHz at room temperature. At cryogenic temperature (77.5K), the switch has an insertion-loss less than 0.6 dB with isolation better than 24 dB up to 50 GHz. The effects of cryogenic temperatures on actuation voltage and contact resistance have been noted. The theoretical and experimental results of the switch performance are presented and compared.

A W-band balun integrated probe with common mode matching network

There has been a growing interest in developing differential Millimeter-wave Monolithic Integrated Circuits (MMICs) in recent years. The characterization infrastructure for these differential devices however, is still limited at higher frequencies. In this paper, a balun integrated probe is designed to cover the entire W-band (75 - 110 GHz) with the potential to be scaled to even higher frequencies. Test structures of the balun are characterized and found to agree well with simulated results for the entire W-band, while the balun integrated probe is characterized from 90 to 115 GHz, also agreeing well with simulation. Over the frequency range measured, the balun integrated probe has lower than -22 dB coupling between the single-ended input and common mode output, as well as between the common and differential modes. Furthermore, the return loss for the differential output and single-ended input modes are better than 10 dB, while the common mode return loss is also better than 10 dB.