You Qian

Development of stress-induced curved actuators for a tunable THz filter based on double split-ring resonators

Using stress-induced curved cantilevers to form double split-ring resonator (DSRR) in three-dimensional configuration, an electrically tunable microelectromechanical system (MEMS) based out-of-plane metamaterials THz filter is experimentally demonstrated and characterized. While the achieved tunable range for the resonant frequency is 0.5 THz at 20 V bias, quality factor of the resonant frequency is improved as well. This MEMS based THz filter using released DSRR structures shows its potential in tunable metamaterials applications such as sensors, optical switches, and filters.

A dual-silicon-nanowires based U-shape nanoelectromechanical switch with low pull-in voltage

A dual-silicon-nanowires based U-shape nanoelectromechanical switch with low pull-in voltage is fabricated using standard complementary metal-oxide-semiconductor compatible process on silicon-on-insulator wafer. The switch consists of a capacitive paddle with dimension of 2 μm by 4 μm supported by two silicon nanowires, suspended on top of the substrate with a gap of 145 nm. The nanowires are 5 μm long with cross-section of 90 nm by 90 nm. The average pull-in voltage is about 1.12 V and the ratio of the ON/OFF current is measured to be over 10 000. According to the preliminary results, this U-shape structure demonstrates great potential in lowering down the pull-in voltage.

Polarization-sensitive microelectromechanical systems based tunable terahertz metamaterials using three dimensional electric split-ring resonator arrays

We present the design, simulation, fabrication, and characterization of structurally reconfigurable metamaterials showing terahertz frequency tunability with a polarization-sensitivity. The proposed metamaterial structures employ deformable microelectromechanical system based curved cantilevers for tuning the resonance frequency of the electric split-ring resonators. The resonance frequency is observed to be either tunable or non-tunable with the electric field of the incident wave, which is perpendicular or parallel to the split gap of the electric split-ring resonators. This polarization-sensitive characteristic has been demonstrated by both the electromagnetic simulation and the experimental measurement. The observed polarization-sensitive tunability could be used for the development of polarization sensitive and insensitive THz polarimetric devices.

Active control of near-field coupling in conductively coupled microelectromechanical system metamaterial devices

We experimentally report a structurally reconfigurable metamaterial for active switching of near-field coupling in conductively coupled, orthogonally twisted split ring resonators (SRRs) operating in the terahertz spectral region. Out-of-plane reconfigurable microcantilevers integrated into the dark SRR geometry are used to provide active frequency tuning of dark SRR resonance. The geometrical parameters of individual SRRs are designed to have identical inductive-capacitive resonant frequency. This allows for the excitation of classical analogue of electromagnetically induced transparency (EIT) due to the strong conductive coupling between the SRRs. When the microcantilevers are curved up, the resonant frequency of dark SRR blue-shifts and the EIT peak is completely modulated while the SRRs are still conductively connected. EIT modulation contrast of ∼50% is experimentally achieved with actively switchable group delay of ∼2.5 ps. Electrical control, miniaturized size, and readily integrable fabrication process of the proposed structurally reconfigurable metamaterial make it an ideal candidate for the realization of various terahertz communication devices such as electrically controllable terahertz delay lines, buffers, and tunable data-rate channels.

An In-Plane Approximated Nonlinear MEMS Electromagnetic Energy Harvester

This paper presents the fabrication, modeling, and characterization of an in-plane approximated nonlinear MEMS electromagnetic energy harvester (EM-EH) device. The approximated nonlinearity and frequency broadening of the device are realized by incorporating small suspension structures, which introduces the spring hardening effect and thus increases the operating frequency of the device toward a higher frequency interval. From the experimental results, the resonant frequencies during frequency up-sweep have been shifted from the original resonance of 82 Hz to 123.5, 135, and 146.5 Hz, at the accelerations of 1.0, 2.0 and 3.0 g, respectively. The corresponding power densities at resonances are 1.6 × 10-8, 2.8 × 10-8, and 5.6 × 10-8 W/cm3. This paper offers a new design methodology of the approximated nonlinear MEMS EM-EH device.

Microelectromechanically tunable multiband metamaterial with preserved isotropy

We experimentally demonstrate a micromachined reconfigurable metamaterial with polarization independent characteristics for multiple resonances in terahertz spectral region. The metamaterial unit cell consists of eight out-of-plane deformable microcantilevers placed at each corner of an octagon ring. The octagon shaped unit cell geometry provides the desired rotational symmetry, while the out-of-plane movable cantilevers preserves the symmetry at different configurations of the metamaterial. The metamaterial is shown to provide polarization independent response for both electrical inductive-capacitive (eLC) resonance and dipolar resonance at all states of actuation. The proposed metamaterial has a switching range of 0.16 THz and 0.37 THz and a transmission intensity change of more than 0.2 and 0.7 for the eLC and dipolar resonances, respectively for both TE and TM modes. Further optimization of the metal layer thickness, provides an improvement of up to 80% modulation at 0.57 THz. The simultaneously tunable dual band isotropic metamaterial will enable the realization of high performance electro-optic devices that would facilitate numerous terahertz applications such as compressive terahertz imaging, miniaturized terahertz spectroscopy and next generation high speed wireless communication possible in the near future.

Periodic Array of Subwavelength MEMS Cantilevers for Dynamic Manipulation of Terahertz Waves

We experimentally demonstrate the active manipulation of terahertz (THz) waves using a periodic array of electrostatically actuated subwavelength microelectromechanical system cantilevers, which effectively behave like a metamaterial. The design methodology for achieving desired ON- and OFF-state resonance frequencies through electromechanical optimization is presented. The microcantilever metamaterial has a switching range of 0.29 THz and a modulation depth of 60% at 0.59 THz. Utilizing metal layer thickness to optimize the devices, an improvement of 40% is achieved in switching range. The microcantilever metamaterials are highly miniaturized, extremely scalable, and electrically controlled with attractive electro-optic performance. Multiple cantilevers can be placed in a desired fashion to form complex unit cell geometry to realize advanced THz manipulation, such as polarization switching, bandwidth tunable filters, multicolor imagers, and so on.

Fabrication and Characterization of a Vacuum Encapsulated Curved Beam Switch for Harsh Environment Application

A vacuum-encapsulated silicon switch with a curved electrode is characterized for operation in harsh environments. An ultraclean vacuum encapsulation process (episeal) seals the switch after release, providing a pristine operating environment for switching operations. In these devices, the curved beam of the actuator enhances the overdrive voltage tolerance to be more than 100 V. The ON/OFF cycle tests were carried out up to 105 cycles at room temperature, and at least 104 cycles under an elevated temperature of 300°C. Throughout the 300°C tests, an average contact resistance of ~ 28 kΩ is measured, demonstrating the stability of the contact. Finally, high speed pulse I-V monitoring unit was used to observe 13-μs switching speed.

A bi-stable nanoelectromechanical non-volatile memory based on van der Waals force

By using complementary-metal-oxide-semiconductor processes, a silicon based bi-stable nanoelectromechanical non-volatile memory is fabricated and characterized. The main feature of this device is an 80 nm wide and 3 μm high silicon nanofin (SiNF) of a high aspect ratio (1:35). The switching mechanism is realized by electrostatic actuation between two lateral electrodes, i.e., terminals. Bi-stable hysteresis behavior is demonstrated when the SiNF maintains its contact to one of the two terminals by leveraging on van der Waals force even after voltage bias is turned off. The compelling results indicate that this design is promising for realization of high density non-volatile memory application due to its nano-scale footprint and zero on-hold power consumption.

All metal nanoelectromechanical switch working at 300 °C for rugged electronics applications.

An all metal based electrostatic nanoelectromechanical switch has been fabricated using a one mask process. High temperature cycling behavior is demonstrated in a vacuum chamber at 300 °C for more than 28 hours. The compelling results indicate that the design is promising for the realization of rugged electronics with three-dimensional integration.