A design-for-test apparatus for measuring on-chip temperature with fine granularity

We present a design-for-test apparatus for measuring real-time, on-chip heat map images with high granularity. Our test chip implemented an 8 × 8 matrix of temperature sensors on-chip in a 0.18μm process with minimal area and power consumption overhead. We then implemented a test interface for measuring individual temperatures with an off-chip ADC and a custom FPGA-based microcontroller with serial UART and ethernet capabilities. This apparatus was used to animate the variation in temperature across the die over time. While temperature sensors have been integrated extensively in VLSI circuits, a single sensor cannot take accurate measurements across an entire chip. Infrared cameras are excellent for direct measurement of temperature across a die, however with new, so-called 3D integrated circuit technology, an infrared camera cannot measure the temperature inside a three dimensional stack. Since performance, reliability, and power consumption are all related to temperature, operating constraints for temperature must be verified to ensure proper device operation. Our design-for-test apparatus demonstrates that fine-grain, real-time measurements of temperature on-chip can be accomplished in real-time with less than 0.5% area overhead in a 1.5 × 1.5mm² total core area, and less than 1mW power consumption added to the device under test (DUT).