TED-AJ03-304 ACTIVE AND PASSIVE THERMAL IMAGING IN SCANNING THERMAL MICROSCOPY

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Measurement of temperature and thermal property distributions with a nanometer scale spatial resolution is important in various fields such as micro- and nano-electronics, material research, and so on. Scanning Thermal Microscope (SThM) provides topological and thermal images with a spatial resolution of several tens of nanometers by a cantilever with a thermocouple or resistance temperature device. Usually, the SThM passively measures temperature or thermal properties by detecting thermal information through a cantilever tip on a sample and converting it with a calibration curve. However, the passive method has an important issue on accuracy of temperature measurement because measured values are influenced by various factors such as surface temperature, thermal properties, unevenness of sample surface, shapes of the tip, contact force, adsorption layer, and so on. Therefore, we have developed a novel active method for quantitative temperature imaging regardless of variations in thermal conductance at the contact point. In the active method, a thermal feedback control step maintains the cantilever at the same temperature as the sample surface by detecting heat flow along the cantilever and feeding power proportional to it to the cantilever; then cantilever temperature is measured by another sensor on it. The passive method has the advantages of systemic simplicity and rapid response. On the other hand, the active method affords accuracy in temperature measurement : it can measure real temperature in principle as long as the thermal conductance has a finite value, no matter how it changes. We experimentally examined the active method by producing multi-function cantilevers and a feedback circuit. The cantilevers have a heat flow sensor, electric heater and a temperature sensor on their small silicon dioxide bodies, as shown in Fig. A1. The active system with sufficient heat flow detection sensitivity demonstrated good performance in real temperature measurement regardless of thermal conductivity differences among samples. The measurement system showed a thermal response of about 50Hz when the cantilever contacts on a tiny thin film resistor on the SThM under a vacuum condition. Furthermore, imaging tests demonstrated performance of the active method. Figure A2 shows a result of topological and thermal images of chromium strips by passive and active methods. Maximum temperature in the active method agreed well with strip temperature measured from electric resistance. It shows that the feedback system compensates variation of contact conductance. Now, we have two thermal imaging modes in the SThM with nano-scale spatial resolution : one is the passive mode with a fast and easy thermal imaging capability, the other is the active mode with quantitative temperature imaging capability.[figure]
一般社団法人日本機械学会の論文
2003-00-00

TED-AJ03-304 ACTIVE AND PASSIVE THERMAL IMAGING IN SCANNING THERMAL MICROSCOPY

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