Thermal transient mapping systems for integrated semiconductor devices and circuits.

Aim of this paper is to present two systems for the acquisition of dynamic thermal maps of ICs, developed at the University of Naples "Federico II", Department of Electronic Engineering and Telecommunication (DIET). First of the two is a system that measures the infrared radiation emitted by a device or an electronic system undergoing a periodic electro-thermal transient, with a time resolution in the order of 2 µs and a temperature resolution in the order of 100 mK. The second system exploits the thermo-optic effect to measure the superficial temperature with a time resolution in the order of tenths of nanosecond and a temperature resolution of some Kelvin, along with a much better spatial resolution with respect to the other. The interaction between thermal and electrical parameters can lead to positive feedback effects that can cause malfunction or even instability and damage in electronic devices. This is the reason why modern power devices design is getting more and more concerned about the electro thermal dynamics of integrated devices and circuits. Besides this, modern day power devices and integrated circuits are getting always faster and smaller causing the electro-thermal phenomena to be much more difficult to follow in time and very localized in space. This is the reason why commercial FPA which are somewhat limited in their spatial and time resolution must be substituted by a single sensor approach. This means that the acquisition have to be repeated a several number of times focusing different spots of the device surface if we aim to retrieve a full map of temperature, but it’s the price to be paid in order to achieve the demanding performances of ICs thermal imaging. Speaking about methods of investigation, many have been exploited for this purpose, each one with its peculiar features and benefits. A concise description of the most common thermal imaging techniques is given in the following. 1.1. Liquid Crystals Some cholesteric materials exhibit, when heated, a mesomorphic state with peculiar optic characteristics especially if deposited in thin layers. The change in colour of these materials can be related to the temperature variation on the surface of an electronic device. This is a very simple and cheap technique that can give good temperature and spatial resolutions but it is inherently slow and, being absolutely not contactless, it alters the boundary conditions of the thermal phenomenon.