Novel processes improve on-chip inductors

Edited by the Electronicstalk editorial team Apr 2, 2003

IMEC has developed wafer-level packaging techniques on top of state-of-the-art back-end-of-line IC processes to realise cost-effective high-Q inductors.

IMEC has developed wafer-level packaging techniques on top of state-of-the-art back-end-of-line IC processes to realise cost-effective high-Q inductors.

The technology is particularly of interest for RF and microwave systems.

The low Q (quality) factors (typically 5 to 10) of traditional on-chip inductors are an important roadblock in the further development of silicon-based technologies at RF and microwave frequencies.

IMEC has developed a novel technique for the realisation of inductors on top of processed ICs: by post-processing wafer-level thin-film layers of Cu metallisation and low-k dielectrics on top of the passivation of state-of-the-art five metal layer back-end-of-line Cu/oxide wafers, Q-factors above 30 can be obtained.

Target frequencies of the thin-film inductors cover the 1 to 20GHz frequency range.

A 1nH spiral inductor with a Q factor topping 30 in a frequency range from 2.6 to 8.6GHz has been demonstrated with a peak Q of 38 around 4.7GHz and resonance frequency of 29GHz.

The combination of post-processed passives with patterned ground shields underneath the spiral inductors, further increases the Q factor and significantly extends the performance of the spiral inductors towards higher frequencies.

The post-processing is compatible with both Al and Cu back-end and induces no performance shift in the underlying interconnect layers and devices.

As thin-film wafer-level packaging techniques are used, the solution is cost effective and consumes no additional silicon real estate.

Furthermore, models for the inductors are available enabling codesign of post-processed inductors and the RF circuit.

With this wafer-level post-processing technique, IMEC has created new opportunities for cost-effective highly integrated high-performance RF and microwave ICs.

Moreover, these ICs can be mounted and interconnected using IMEC's multilayer thin-film technology to produce high-performance miniature system-in-a-package solutions for wireless telecommunication applications.