HIGH FREQUENCY NOISE SOURCES EXTRACTION IN NANOMETIQUE MOSFETs

摘要

The continuing down-scaling of MOSFET's make their noise properties to be more and more fundamentals, for some difficulties may happen when considering high frequency applications. Indeed, though the intrinsic noise performances of MOSFET's are very promising, the technological process inherent to such devices when the device is scaling down makes de facto parasitic elements (such overlap capacitances, gate resistances) to limit greatly the f_(max) (maximum oscillation frequency) and then the noise performances of the device. Also, potential mismatch in Low Noise Amplifiers (LNA) along with the use of high losses Silicon Substrate may increase greatly the noise figure of the LNA, that will be much higher than the minimum noise figure of the stand alone device. As a general trend, the decrease of device's dimensions along with the decrease of the DC supply voltage will require in the future to have the availability of more and more accurate thermal (and related diffusion) noise models. These noise models can be issued from device physics models but also can be extracted from experimental noise measurements ; in such a case, one wants to perform accurate measurements of the noise parameters F_(min), R_n and Γ_(opt) of the Device Under Test (DUT). A lot of methods are available in the literature, we will focus here upon the one used in routine in our laboratory, which is based on noise figure measurements in a 50 Ω environment and physical considerations. The presentation of the NF_(50), method will be re-called prior describing the problems related to an accurate extraction of the noise sources. These problems will address, by the use of a physical noise modeling, a discussion related to the theoretical assumption (uncorrelated noise sources) made to extract the four noise parameters from the NF_(50) data versus frequency. Due to the low resistivity silicpn wafers used for such characterization, we will also pay attention towards the specific de-embedding noise procedure which needs to be used.'