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This paper demonstrates a distributed de-embedding technique to derive accurate models for on-chip passives. Due to the inherently large pitch of on-wafer probes, interconnect lengths between bondpads and the device under test (DUT) of several hundreds of mum are often unavoidable for inductors and transmission lines. At frequencies above 10 GHz, the length of such interconnects becomes significant with respect to the wavelength. The impedance transformation through the lines between DUT and bondpads is not taken into account in the standard Open-Short de-embedding technique. Moreover, the impedance of the open de-embedding is lumped to a single parallel impedance located at the bondpad. This approach is not accurate at frequencies above 10 GHz. Distributed techniques are known that improve accuracy. However, these require the use of dedicated transmission line de-embedding structures. In this paper, a method is demonstrated to derive a transmission line de-embedding model from standard Open-Short de-embedding structures. The sub-optimum de-embedding design showed a slowing factor of radic(11) which was due to regular holes in the metal shield underneath the signal lines. Guidelines for the design of optimum de-embedding structures are provided.
Date of Conference: 12-14 Oct. 2009