A scanning thermal microscope is used to study the temperature distribution on the gate surface of a MOS structure submitted to an electric stress. Over a threshold of stress current intensity, hot spots have been observed and then numbered versus stress conditions. The data analysis shows that the hot spots number depends on injected current and also on the MOS structure degradation history. The temperature map of the gate surface is riddled with hot spots since the sample breakdown. Otherwise, hot spots seem to appear in privileged areas like the gate borders. On the basis of the literature, our observations lead us to conclude that hot spots result of degradations inside the structure.
We have studied temperature variations on two dissipative structures with two different techniques. The dissipative structures are constituted of thin (0.35µm) dissipative resistors, the distance between two resistors being equal to 0.8 or 10 µm. On one hand, we have used a thermoreflectance imaging technique which is a well-known non contact optical method to evaluate temperature variations but whose spatial resolution is limited by diffraction. On the other hand, we have used a Scanning Thermal Microscope (SThM) to study the thermal behaviour of these small dissipative structures. We compare qualitative results obtained by both methods and we present their advantages and limitations for temperature measurements on microelectronic devices.
We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero.