6W/25mm2 inductive power transfer for non-contact wafer-level testing

Wafer-level testing allows detection of manufacturing errors and removes non functional devices early in the fabrication process. It is commonly performed by placing a probe card directly above a device under test (DUT) and establishing a mechanical contact between them by means of an array of probes. This is an invasive technique that may damage fragile low-k dielectric layers and deform pads or bumps. More importantly, it is very difficult to flip thinned wafers face up for probing if they were earlier positioned face down for back grinding. Additional difficulty in handling of thinned wafers arises if dies have to be flipped again for bumping. One solution to above problems is wireless probing. With a number of proposed techniques for establishing high-speed inductive-coupling data links and measuring DC analog signal wirelessly, the largest remaining obstacle to non-contact wafer-level testing is supplying power to the DUT. This is because wireless power transfer solutions reported earlier do not provide an output power that is sufficient for testing modern high performance devices.This paper presents an inductive power transfer system that is capable of delivering up to 6W of DC power to the on-chip load. The system is partitioned into 8 power transfer channels, each containing two cir cuits: a power transmitter implemented in the probe card, and an on-chip power receiver. This paper focuses on the design of the power receiver, as the receiver performance limits the output power of the whole system.