In order to reduce production costs of RF devices, it is important to remove bad circuits very early in the production flow. It is all the more true for dies designed to be integrated in complex systems. Thus highly efficient RF wafer testing is mandatory for those applications to prevent the loss of assembled systems due to defective RF dies. The problem is that current RF probing technologies hardly fulfill the industrial test requirements in terms of accuracy, reliability and cost. The proposed method proves to be a very interesting alternative to validate RF parameters with no need of expensive RF equipments (RF probes and RF automated test equipments (ATE)). A new test strategy based on DC or very low frequency (LF) measurements, which allows the elimination of expensive RF tests, is presented. The main idea is to insert some simple design for test (DfT) circuitry within the chip.This DfT provides relevant information on the structural behavior of the device blocks. The internal node data are additional to standard DC test measurements like power supply current or advanced DC test signatures (e.g. Vdd ramping), and LF measurements like gain in loopback mode.Since RF performance of each block is directly related to such structural data, it is possible to predict the RF characteristics of the blocks without time consuming RF measurements. RF parameters estimation is performed using nonlinear Artificial Neural Networks.

ISBN 978-1-4244-5834-9International audienceThe paper discusses a variety of sensors to enable a built-in test in RF devices. The list of sensors includes dummy circuits, process control monitors, DC probes, an envelope detector, and a current sensor. Dummy circuits and process control monitors are simple circuits that do not tap into the signal path of the RF device. Instead, they monitor the device by virtue of being subject to the same process variations. Their outputs form an alternative measurement pattern which can be mapped to the performances of the device using a typical alternate test flow. The rest of the sensors are physically connected to the RF device, thus they can detect random catastrophic defects within it and, as an auxiliary benefit, they can improve the accuracy in predicting its performances. The degradation that these sensors incur is carefully assessed and the RF device is co-designed with them to correct for the losses. The operation and test efficiency of the sensors is demonstrated for the case of an RF LNA using post-layout simulations

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ISBN 978-1-4673-1594-4International audienceThis paper discusses a new type of sensors to enable a built-in test in RF circuits. The proposed sensors provide DC or low-frequency measurements, thus they can reduce drastically the testing cost. Their key characteristic is that they are nonintrusive, e.g. they are not connected electrically to the RF circuit. Thus, the performances of the RF circuit are unaffected by the monitoring operation. The sensors function as process monitors and share the same environment with the RF circuit. The underlying principle is that the sensors and the RF circuit are subject to the same process variations, thus shifts in the performances of the RF circuit can be inferred implicitly by shifts in the outputs of the sensors. We present experimental results on fabricated samples that include an LNA with embedded sensors. The samples are collected from different sites of a wafer such that they exhibit process variations. We demonstrate that the performances of the RF circuit can be predicted with sufficient accuracy through the sensors by employing the alternate test paradigm

International audienceThis article proposes a new class of sensors for built-in test in RF devices. These sensors are placed in close proximity to the DUT on the same substrate without being electrically connected to it. Instead, they monitor it by virtue of being subjected to the same process variations. The authors also describe other types of sensors they have studied, including DC probes, an envelope detector, and a current sensor