Design and modeling of a micromachined high-Q tunable capacitor with large tuning range and a vertical planar spiral inductor

Jinghong Chen, Jun Zou, Chang Liu, José E. Schutt-Ainé, Sung Mo Steve Kang

Research output: Contribution to journalArticlepeer-review


In wireless communication systems, passive elements including tunable capacitors and inductors often need high quality factor (Q-factor). In this paper, we present the design and modeling of a novel high Q-factor tunable capacitor with large tuning range and a high Q-factor vertical planar spiral inductor implemented in microelectromechanical system (MEMS) technology. Different from conventional two-parallel-plate tunable capacitors, the novel tunable capacitor consists of one suspended top plate and two fixed bottom plates. One of the two fixed plates and the top plate form a variable capacitor, while the other fixed plate and the top plate are used to provide electrostatic actuation for capacitance tuning. For the fabricated prototype tunable capacitors, a maximum controllable tuning range of 69.8% has been achieved, exceeding the theoretical tuning range limit (50%) of conventional two-parallel-plate tunable capacitors. This tunable capacitor also exhibits a very low return loss of less than 0.6 dB in the frequency range from 45 MHz to 10 GHz. The high Q-factor planar coil inductor is first fabricated on silicon substrate and then assembled to the vertical position by using a novel three-dimensional microstructure assembly technique called plastic deformation magnetic assembly (PDMA). Inductors of different dimensions are fabricated and tested. The S-parameters of the inductors before and after PDMA are measured and compared, demonstrating superior performance due to reduced substrate loss and parasitics. The new vertical planar spiral inductor also has the advantage of occupying much smaller silicon areas than the conventional planar spiral inductors.

Original languageEnglish (US)
Pages (from-to)730-739
Number of pages10
JournalIEEE Transactions on Electron Devices
Issue number3
StatePublished - Mar 2003


  • Electrostatic actuation
  • Magnetic actuation
  • Microelectromechanical systems (MEMS)
  • Modeling and simulation
  • Monolithic inductor
  • Quality factor
  • RFIC
  • Self-resonance
  • Varactor
  • Variable capacitor

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering


Dive into the research topics of 'Design and modeling of a micromachined high-Q tunable capacitor with large tuning range and a vertical planar spiral inductor'. Together they form a unique fingerprint.

Cite this