Temperature Distribution Analysis of CMOS LSI With On-Chip Sensing Device Arrays

A test structure for analysis of temperature distribution in CMOS LSI is presented. Fundamental thermal properties of LSI chip have been measured and discussed with simulation results. The test structure consists of 24 sensor blocks, each of which has a resistor as an on-chip heater, a p-n diode or n-MOSFET array for temperature sensing and selector switches. Dependence of heating time and distance from the resistor are analyzed as well as transient phenomena. Temperature $T$ decreases with the distance $L$ , is proportional to the reciprocal of $L~(1/L)$ , and empirical equations have been proposed. The results of both p-n diode and n-MOSFET sensors are nearly the same. A thermal simulation gives an $L$ dependence of $T$ similar to the measured result. $T$ of 160 pin QFP becomes lower than that of 80 pin due to its larger outline, but $L$ dependence of $T$ is similar. The abrupt and gradual change of $T$ at the heater switching suggests both fast and slow processes in thermal conduction. The test structure can provide an effective methodology for analysis of fundamental thermal properties in LSIs packaged in various ways.