sábado, 20 de marzo de 2010

Multi Layer MEMS Transformer and MEMS Filter

Multi metal layer fabrication technology is crucial in future developments of RF-MEMS devices. This is
due to high density requirement of the devices while keeping their Q-factor high [1,2]. In this paper, the
use  of surface micromachining techniques for fabricating multi metal layer RF MEMS devices is
presented. Two types of these devices, namely micro-transformer and micro-filter are exemplified.
MEMS transformer fabricated in IMEN-UKM is a square spirally  interwinding planar coil, as
depicted in Fig. 1. It consists of two coil structures stacked on top of each other and connected by vias.
The metal used is aluminum (sh=26.5 mΩ/sq), which  is deposited by multi  layer deposition  technique
using vacuum evaporation (Evaporated MML method). Fig. 2 shows the resistance characteristics of the
device for various metal thicknesses, when excited up to 1 Mhz operating frequency. It is shown that the
increase of metal thickness significantly affects the decrease of coil resistance. As shown in Fig. 3, the
maximum gain is found at frequency range between 3 and 5 MHz for all metal thicknesses. It can also be
seen that increasing metal thickness increases gain. The transformers work effectively at frequency range
between 1 and 10 MHz due to the high capacitive effects of the stacked structured coil.  
MEMS bandpass filter fabricated in IMEN-UKM is a  two-resonator system, which manipulates
electrical coupling between two symmetrical clamped–clamped micromechanical resonators. The filter
depicted in Fig. 4 has center frequency of 180 kHz, coupling capacitance of 17.7fF, bandwidth of 400
Hz, 20-dB shape-factor of 3.6, and insertion loss of 8-dB. Fig. 5 shows a close-up view of the multi-
stacked aluminum  layer of the resonator, which is fabricated using the same technique as the MEMS
transformer presented above. Fig. 6 plots the transmission characteristics of the filter. It is observed that
the Q-factor depends on the resonator's motional resistance, operating frequency, filter bandwidth, and
tolerable passband ripple.
This work was supported by the Malaysian Ministry of Science and Technology, under  GUP  Project

Emmanuel Rodriguez
Fuente: http://www.nanotechmalaysia.com.my/images/Sample%20of%20extended%20abstract.pdf

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