A Method for Attenuating the Spurious Responses of Aluminum Nitride Micromechanical Filters

Abstract

We present a method for attenuating the spurious responses in aluminum nitride micromechanical filters and demonstrate the technique in a 4-pole self-coupled filter operating at 494 MHz. In the standard implementation of a 4-pole self-coupled filter, each filter pole is realized using physically identical resonators. The spur mitigation approach reported here realizes the four poles of the filter using two different physical implementations of the resonator. Both resonators are designed to have identical responses at the desired resonant frequency of 494 MHz, while many of the spurious responses of the two resonators appear at nonidentical frequencies and do not add constructively at the filter output. Using the reported method, the measured attenuation of the largest filter spur is increased by 47.5 dB when compared with a 4-pole filter realized using identical resonators (standard approach) to form each filter pole. The filter realized using the reported spur attenuation approach has >59.6 dBc of stopband and spurious response rejection over nearly a 2-GHz frequency span.[2013-0342]

MEMS switching of contour-mode aluminum nitride resonators for switchable and reconfigurable radio frequency filters

“…Energy is confined to the resonator by sidewalls that are etched through A six-finger switched resonator is shown in the optical image in figure 6(a), which also shows the fixed resonator on which the design is based in figure 6(b). The fixed width-extensional resonators provide a comparison to a resonator which has been used previously to demonstrate three-and four-pole filters operating near 500 MHz with 50 Ω impedance [20]. The devices reported here do not a use a SiO 2 temperature compensation layer, resulting in a higher frequency of 635 MHz for the same dimensions.…”

Hybrid Acoustic-Wave-Lumped-Element Resonators (AWLRs) for High-<formula formulatype="inline"><tex Notation="TeX">$Q$</tex> </formula> Bandpass Filters With Quasi-Elliptic Frequency Response

“…In yet another way, the magnitude of the spurious modes can be reduced by increasing the filter order. In particular, as recently shown by Olsson et al in [32], the use of multiple resonators with identical center frequencies and a relative offset between their spurious modes may result in an overall filter response with highly attenuated spurious frequencies. Nevertheless, such a study falls out of the scope of this work.…”

“…6). It is apparent that broader bandwidths can be realized by either suppressing the undesired spurious modes or by increasing their separation from the fundamental mode, as discussed in [13], [14], [31], and [32].…”

Single and Multiband Acoustic-Wave-Lumped- Element-Resonator (AWLR) Bandpass Filters With Reconfigurable Transfer Function

“…This model can be extracted through the design methodology described in [12] in which additional series-resonant-type branches need to be added in parallel to the fundamental resonance. Acoustic-wave resonators with improved RF performance in terms of spurious suppression-geometrical optimization of anchor points, ID fingers, and material orientation in [29] and [30]-or enlarged separation from the resonant mode-in-series cascade of acoustic-wave resonators with slightly shifted higher order modes and resonator arrays in [31] and [32]-have been reported in [29]- [32]. However, such design methodologies are out of the scope of this paper.…”