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Heat observations
Heat observations
Heat generation in electronic devices has been an ongoing problem since the inception of electronic devices and their applications. Anyone can feel the heat in an electronic product by hand or with a simple thermometer, and it's pretty easy to see where the heat is coming from. However, it's not always easy to go a step further and determine which chipset is generating the heat, or which microprocessors are particularly hot. While macroscopic temperatures can be observed with a simple thermometer, observing temperatures at the microstructure level is a different story.
Fever thermometers and IR cameras, which we became familiar with during the 2019 coronavirus pandemic, are suitable products and methods for macroscopic temperature observation. IR cameras measure temperature using infrared light (near IR 800 nm to far IR 10,000 nm or more), which is outside the visible light region, so it is very difficult or impossible to observe heat generated at the micrometer level or smaller. Therefore, since most of the aforementioned electronic devices are smaller than a micrometer in size, it is difficult to observe heat using infrared thermography methods with wavelengths greater than 1,000 nm.
The thermal reflection microscope (TRM), jointly developed by the research team, Nanoscopesystems, and KBSI, was successfully used to observe the heat generated in microstructures. The TRM method has a spatial resolution of less than 0.1 μm and a temperature resolution of 0.1 C or less.
There are a variety of measurement tools for measuring heat in microscale devices, including the aforementioned infrared thermography, micro-Raman thermography, and scanning thermal microscopy methods. While each of these methods has its advantages in measuring temperature, they limit their applicability in terms of spatial resolution and convenience in ways that make them unsuitable for thermal analysis of microscale and sub-microscale devices.
Electrical measurements of 5 μm x 10 μm devices measured heating in the center, where current density is as high as possible. While 5 μm x 10 μm is not a microscopic device, the thermal measurements show heat distribution in a very small spatial area. The measured device is a 500 nm thick poly-silicon film deposited with n-type doping for high electrical conductivity.
Thermal reflection microscopy reveals the heat generated in a localized area of the device, which is a very fine localized area. We observed that heat is generated in a narrow bridge area in the center and spreads to the left and right.
Measurements of the heat generated by semiconductor transistors are generally not well reported. This is because most transistors have very small channel lengths and widths, and the tools to measure the heat in such small areas are either lacking or limited. The figure on the left shows the heat generated by a transistor measured with an IR camera. It can be seen by the brightness that the heat is generated in the channel. The yellow color of the probe tip and background is due to the fact that the measurement is not calibrated. On the other hand, in the data shown on the right, you can clearly observe the spreading phenomenon of heat generated in the channel. By applying a high voltage to the drain electrode, we can observe that the heat spreads from the drain electrode. The observation data on the right is the result of measurement using TRM.
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