Interleaved 3D On-Chip Differential Inductor And Transformer

Tech ID: 27288 / UC Case 2005-370-0


UCLA researchers in the Department of Electrical Engineering have developed an interleaved three-dimensional (3D) on-chip differential inductors and transformers used in silicon based radio frequency/millimeter wave integrated circuits


On-chip inductors and transformers are key passive components in radio frequency/millimeter wave integrated circuits (RF/MMICs). It is desirable to design and fabricate on-chip inductors and transformers with small size, high quality factor, large inductance, high coupling efficiency and high self-resonating frequency. In silicon based integrated circuits where the substrate is lossy, it is crucial that the on-chip inductors and transformers consume minimal real estate, so as to reduce parasitic capacitance and increase self-resonating frequency.


UCLA researchers developed a new interleaved three-dimensional (3D) on-chip differential inductors and transformers design. By separating each turn of the coil into two partial windings and placing them interleaved in different layers, one can realize on-chip inductors and transformers with the desired characteristics mentioned above. The interleaving configuration here refers to two coils sharing a common axis and running generally parallel to each other in which adjacent partial windings of the coils are separated spatially to reduce parasitic capacitance.


On-chip differential inductors used in RF/MMICs with differential structures

  • Amplifiers
  • Mixers
  • Voltage controlled oscillators (VCOs)
  • Phase-locked loops (PLLs)/synthesizers
  • Frequency dividers


  • Miniature size which consumes very small chip real estate
  • Less parasitic capacitances between the inductor and the substrate and among windings of the inductor and transformer itself
  • Large inductance which increases the Q factor inductance product
  • High coupling efficiency between the primary and the secondary coil of on-chip transformers
  • Very high self-resonating frequency which is desirable in high frequency applications
  • A symmetrical structure which is inherently compatible with differential circuits
  • The transformers induce less phase mismatch errors in quadrature circuits than two un-correlated inductors

State Of Development

The UCLA researchers have designed, simulated and implemented an interleaved three-dimensional (3D) on-chip differential inductors and transformers. The design includes coils interleaved to separate adjacent windings, as well as method for making the three-dimensional on-chip differential inductors. The circuits have been applied to the design of low noise amplifier (LNA), mixer, coupled VCO arrays, and frequency dividers. All these circuits have been simulated and implemented in silicon. A US patent has been granted for this invention.

Related Materials

Patent Status

Country Type Number Dated Case
United States Of America Issued Patent 8,325,001 12/04/2012 2005-370


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  • Chang, Mau-Chung Frank

Other Information


On-chip, three-dimensional, 3D, differential, inductor, transformer, interleave, radio frequency, RF, millimeter wave integrated circuits, MMICs, Q factor, coupling efficiency, self-resonating frequency, parasitic capacitance, CMOS, BiCMOS, SiGe

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