RESUMO
This paper presents a new metal-contact RF MEMS switch based on an Al-Sc alloy. The use of an Al-Sc alloy is intended to replace the traditional Au-Au contact, which can greatly improve the hardness of the contact, and thus improve the reliability of the switch. The multi-layer stack structure is adopted to achieve the low switch line resistance and hard contact surface. The polyimide sacrificial layer process is developed and optimized, and the RF switches are fabricated and tested for pull-in voltage, S-parameters, and switching time. The switch shows high isolation of more than 24 dB and a low insertion loss of less than 0.9 dB in the frequency range of 0.1-6 GHz.
RESUMO
The silicon etching process is a core component of production in the semiconductor industry. Undercut is a nonideal effect in silicon dry etching. A reduced undercut is desired when preparing structures that demand a good sidewall morphology, while an enlarged undercut is conducive to the fabrication of microstructure tips. Undercut is related to not only the production parameters but also the mask materials. In this study, five mask materials-Cr, Al, ITO, SiNx, and SiO2-are chosen to compare the undercut effect caused by the isotropic etching process and the Bosch process. In the Bosch process, the SiNx mask causes the largest undercut, and the SiO2 mask causes the smallest undercut. In the isotropic process, the results are reversed. The effect of charges in the mask layer is found to produce this result, and the effect of electrons accumulating during the process is found to be negligible. The undercut effect can be enhanced or suppressed by selecting appropriate mask materials, which is helpful in the MEMS process. Finally, using an Al mask, a tapered silicon tip with a top diameter of 119.3 nm is fabricated using the isotropic etching process.
RESUMO
I Microhotplates are critical devices in various MEMS sensors that could provide appropriate operating temperatures. In this paper, a novel design of poly-Si membrane microhotplates with a heat compensation structure was reported. The main objective of this work was to design and fabricate the poly-Si microhotplate, and the thermal and electrical performance of the microhotplates were also investigated. The poly-Si resistive heater was deposited by LPCVD, and phosphorous doping was applied by in situ doping process to reduce the resistance of poly-Si. In order to obtain a uniform temperature distribution, a series of S-shaped compensation structures were fabricated at the edge of the resistive heater. LPCVD SiNx layers deposited on both sides of poly-Si were used as both the mechanical supporting layer and the electrical isolation layer. The Pt electrode was fabricated on the top of the microhotplate for temperature detection. The area of the heating membrane was 1 mm × 1 mm. Various parameters of the different size devices were simulated and measured, including temperature distribution, power consumption, thermal expansion and response time. The simulation and electrical-thermal measurement results were reported. For microhotplates with a heat compensation structure, the membrane temperature reached 811.7 °C when the applied voltage was 5.5 V at a heating power of 148.3 mW. A 3.8 V DC voltage was applied to measure the temperature distribution; the maximum temperature was 397.6 °C, and the area where the temperature reached 90% covered about 73.8% when the applied voltage was 3.8 V at a heating power of 70.8 mW. The heating response time was 17 ms while the microhotplate was heated to 400 °C from room temperature, and the cooling response time was 32 ms while the device was recovered to room temperature. This microhotplate has many advantages, such as uniform temperature distribution, low power consumption and fast response, which are suitable for MEMS gas sensors, humidity sensors, gas flow sensors, etc.
