Yan-qing Zhu

A Novel Three-State RF MEMS Switch for Ultrabroadband (DC-40 GHz) Applications

Design, fabrication, and measurement results of a lateral dc-contact RF microelectromechanical systems switch for ultrabroadband applications are presented in this letter. The switch is driven by a bidirectional cascaded electrothermal actuator, which can generate larger displacements and contact forces at two directions than traditional electrothermal actuators. Because of this bidirectional actuator, the proposed switch can not only realize the off-state to on-state shifting, but also provide an additional deep off-state. The proposed switch is fabricated by MetalMUMPs process, and measurement results show that the insertion loss is less than -0.5 dB and the initial isolation is better than -22.5 dB at 0-40 GHz range. At the deep off-state, the isolation better than -30 dB can be achieved at the whole frequency range 0-40 GHz. The measurement results agree well with the theory and design.

Development of a self-packaged 2D MEMS thermal wind sensor for low power applications

This article describes the design, fabrication, and testing of a self-packaged 2D thermal wind sensor. The sensor consists of four heaters and nine thermistors. A central thermistor senses the average heater temperature, whereas the other eight, which are distributed symmetrically around the heaters, measure the temperature differences between the upstream and downstream surface of the sensor. The sensor was realized on one side of a silicon-in-glass (SIG) substrate. Vertical silicon vias in the substrate ensure good thermal contact between the sensor and the airflow and the glass effectively isolates the heaters from the thermistors. The substrate was fabricated by using a glass reflow process, after which the sensor was realized by a lift-off process. The sensors geometry was investigated with the help of simulations. These show that narrow heaters, moderate heater spacing, and thin substrates all improve the sensors sensitivity. Finally, the sensor was tested and calibrated in a wind tunnel by using a linear interpolation algorithm. At a constant heating power of 24.5 mW, measurement results show that the sensor can detect airflow speeds of up to 25 m s−1, with an accuracy of 0.1 m s−1 at low speeds and 0.5 m s−1 at high speeds. Airflow direction can be determined in a range of 360° with an accuracy of ±6°.

Sensitivity Improvement of a 2D MEMS Thermal Wind Sensor for Low-Power Applications

In this paper, we report a novel and low-cost method to improve the sensitivity of a low-power 2D microelectromechanical systems thermal wind sensor by using HF wet etching. After wet etching, the thickness of the glass substrate decreases, so that the sensors thermal vias become more exposed to the wind. As a result, the conductive heat transfer is weakened and the convective heat transfer is enhanced in sensor operation. Finite-element method simulations verify this analysis. Moreover, the sensor chips with different lengths of silicon vias above the substrate are successfully fabricated and tested. Measurement results show that the wet etching has no influence on the metal film sensing and heating elements of the sensor. Besides, before and after wet etching for 7 and 14 min, at the wind speed of 5 m/s, the measured sensitivities of the sensor with a total power consumption of 24.5 mW are 77.2, 98.6, and 164.1 mK/(m/s). Measurement results also show that the improved sensitivity of the sensor chip can provide a more accurate measurement in wind speed but has little effect on the wind direction measurement. Instead, the accuracy of wind direction measurement is mainly related to the structural and thermal symmetries of the wind sensor. After compensation, the proposed thermal wind sensor can detect the wind direction in a full range of 360° with an mean error of 2.3° and a maximum error of 6°.

Effects of Ambient Humidity on a Micromachined Silicon Thermal Wind Sensor

The effect of ambient humidity on a micromachined silicon 2-D thermal wind sensor has been investigated. The sensor includes a central heater and four temperature sensors. It measures the flow-induced temperature gradient on the heated surface. Properties of the ambient air, such as density, viscosity, heat conductivity, and specific heat capacity, are theoretically presented to explore their effects on the performance of the sensor at different relative humidity levels. The output of the sensor as a function of wind speed at different relative humidity levels has been measured. It shows that there is a measurable effect at both high relative humidity and temperature. The results presented here provide a valuable reference for the practical applications of the wind sensor.

Temperature Effects on the Wind Direction Measurement of 2D Solid Thermal Wind Sensors

For a two-dimensional solid silicon thermal wind sensor with symmetrical structure, the wind speed and direction information can be derived from the output voltages in two orthogonal directions, i.e., the north-south and east-west. However, the output voltages in these two directions will vary linearly with the ambient temperature. Therefore, in this paper, a temperature model to study the temperature effect on the wind direction measurement has been developed. A theoretical analysis has been presented first, and then Finite Element Method (FEM) simulations have been performed. It is found that due to symmetrical structure of the thermal wind sensor, the temperature effects on the output signals in the north-south and east-west directions are highly similar. As a result, the wind direction measurement of the thermal wind sensor is approximately independent of the ambient temperature. The experimental results fit the theoretical analysis and simulation results very well.

A self-packaged self-heated thermal wind sensor with high reliability and low power consumption

A self-packaged self-heated thermal wind sensor was designed, fabricated and measured for the first time in this paper. To achieve a low power and reliable sensor, a newtype silicon-in-glass (SIG) substrate with anisotropic thermal conductivity was introduced. In this substrate, the embedded vertical silicon vias are used to realize the thermal interconnections between the sensor and the wind, while the horizontal thermal conduction between the thermistors is isolated effectively by the glass. The substrate is based on a glass reflow process and the sensor was fabricated on this substrate by using a lift-off process. The whole process only need three masks. At last, we performed a wind tunnel test in constant voltage (CV) mode, and the measurement results show that the thermal wind sensor can measure wind speeds up to 17.5 m/s, and the measured sensitivities of the sensor with different applied voltages of 0.8 V, 0.9 V, and 1 V are respectively 6.3 mV/(m/s), 9.52 mV/(m/s), and 14.17 mV/(m/s) at zero-flow point. The corresponding power consumption of the sensor with different voltages are respectively 12.3 mW, 15.57 mW and 19.23 mW. Measurement results also show that wind direction in a full range of 360° with an error less than 6° could be obtained.

Development of a robust 2-D thermal wind sensor using glass reflow process for low power applications

In this paper, a low-power MEMS two-dimensional (2-D) thermal wind sensor with high reliability is presented. The sensor is based on a glass-in-silicon reflow process. The embedded vertical silicon vias in the glass substrate are used to realize the electrical connections between the sensing elements and the electrode-pads, which are respectively placed on on the front and the back surface of the chip. Then, the sensor and the external circuit are connected using the wire-bonding process through the electrode-pads on the back surface. At last, the bonding wires at the backside is encapsulated by polyester paint, protecting the electrical connections of the sensor from the effect of the external environment. In addition, a passivation layer of nitride is deposited on the surface of the wind sensor to prevent direct exposure of the sensing elements to harsh media. The sensor works in a self-heated mode, which makes its power consumption could be reduced into the sub-milliwatt range, offering high initial sensitivity and wide measurement range, respectively. The sensor was tested in a wind tunnel in constant voltage mode. Measurement results show that the thermal wind sensor can measure wind speeds up to 17.5 m/s with a low power consumption of only 4.81 mW. Measurement results also show that wind direction in a full range of 360° with an error within 6° could be obtained.

A tunable high performance microwave equalizer based on RF MEMS switches

The theory, design, fabrication and measurements of a novel tunable equalizer for adjusting the microwave signals based on RF MEMS switches are presented. The novelty of the tunable equalizer is the RF MEMS switches and the thick CPW line with released signal and ground sections based on the MEMS technology. This equalizer adjusts the attenuation curve by the RF MEMS switches and makes the power of the microwave signal flat during the work frequency range. In this method, the equalizer can achieve tunable characteristic, high frequency and good microwave performance. This MEMS equalizer is fabricated by MetalMUMPs process. The experiment results show the MEMS equalizer can adjust two attenuation curves and has low reflection losses, low minimal insertion losses at frequency range from 20GHz~24GHz.

A high performance microwave equalizer based on MEMS technology

The theory, design, fabrication and measurements of a MEMS equalizer for adjusting the microwave signals are presented. The novelty of the equalizer is the CPW line with released signal and ground sections based on the MEMS technology. In this method the work frequency can be achieved higher and the minimal insertion losses can be greatly reduced due to the dielectric losses. The MEMS equalizer is fabricated by MetalMUMPs process. The experimental results show that reflection losses of the MEMS equalizer are below -17dB at the whole frequency range, the minimal insertion losses are around 1dB at 21GHz frequency point and the maximal insertion losses are around 2.7dB at 26.8GHz frequency point. The experimental results agree well with the theory and the simulation.

Effect of packaging asymmetry on the performance of a 2D MEMS thermal wind sensor with different heating geometries

In this paper, the effect of packaging asymmetry on the performance of a 2D MEMS thermal wind sensor with different heating geometries is investigated quantitatively for the first time. The thermal wind sensor is fabricated on a silicon-in-glass (SIG) substrate with anisotropic thermal conductivity by a lift-off process. The silicon vias embed in the glass are employed to exchange heat between the device and the airflow, whereas the glass is used to reduce the invalid heat loss and improve the sensitivity of the sensor chip. In the experiment, the wind sensor was operated by using different heating geometries, which are respectively annular heating geometry, square heating geometry and hybrid heating geometry. Measurement results show that, with different heating geometries (annular, square and hybrid), the mean square errors of the output voltage versus wind direction (0-360 degrees) of the sensor at 30 m/s are respectively 5 mV, 25 mV and 11.67 mV before compensation. The corresponding average direction errors of the sensor are respectively 3.42, 11 and 5.79 degrees. It can be seen that the thermal wind sensor with annular heater geometry is less susceptible to package errors.