MEMS‐based LC tank with extended tuning range for multiband applications

Abstract

This paper presents the modeling, simulations, and measurements of a compact multiband microelectromechanical (MEMS)‐based LC tank resonator suitable for low phase noise voltage‐controlled oscillators (VCOs). The resonator is based on a high‐Q spiral inductor and high capacitance ratio varicap fully integrated in FBK‐irst (Fondazione Bruno Kessler) MEMS manufacturing process. The design of the varicap is based on double‐actuation mechanism with a mechanical central bond that inhibits the pull‐in allowing for a theoretically infinite tuning ratio. The measurements have shown a total not continuous capacitance ratio (Cr) of 5.2 with a continuous variation of the capacitance values in the range 225 fF–600 fF which corresponds to a continuous capacitance ratio (Cr*) of 2.6. The performance repeatability, the power‐handling capability, and the stability over time were tested on 10 samples showing a negligible variation of the capacitance values. The spiral inductor consists of a suspended gold membrane thick 5 µm in a circular shape which was modeled in order to optimize the quality factor (Q) in the frequency range 2–4 GHz. The measurement results show a Q of about 55 in the 2–4 GHz frequency band. The LC tank measurements show an overall tuning range better than of 45% in the 3.2–4.9 GHz frequency band, consisting of two continuous tuning ranges of 7.5% and 25%. The LC tank allowed the design of MEMS‐based voltage‐controlled oscillators (VCOs) with an overall tuning better than 60% in the frequency range 2.15 GHz–3.85 GHz and two separate regions of continuous tuning range. The VCO prototype will be fabricated on Surface Mount Technology on RO4350 laminate. The main figures of merit are presented in comparison with the state of the art.

Mechanical Response of MEMS Suspended Inductors under Shock Using the Transfer Matrix Method

“…The spiral was supported by two pillars on the substrate, which also connected the signal transmission lines. MEMS inductors, which are designed in the same layout but manufactured using different processes, might not be identical in several aspects, including metal thickness, surface flatness, silicon resistivity, silicon dioxide thickness, residual stress [ 38 ], and so on. Here, it is assumed that the three-dimensional dimensions of the metal spiral are the correct sizes in the design layout, in the sense that the spiral strips are cuboids in geometry.…”

50 GHz active‐LC CMOS oscillator: Theoretical study and experimental proofs

“…Note that when the AI is switched off ( V BIAS = 0 V), the equivalent inductance amounts to 118 pH, with a quality factor of 7.3, at 50 GHz. When the AI is switched on ( V BIAS = 0.48 V), the equivalent inductance amounts to 133 pH, with a quality factor exceeding 400, at 50 GHz, i.e., even beyond the typical performance exhibited by solutions based on microelectromechanical structures operating at a few gigahertz [ Cazzorla et al ., ]. The current consumption amounts to 11 mA from a 1.2 V supply.…”