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Thermal Measurement on Silicon Chip

IP.com Disclosure Number: IPCOM000062585D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Kara, BH: AUTHOR [+2]

Abstract

All silicon chips have a PN diode structure for isolation. Firstly, a large current is passed through this isolation diode to heat the chip, followed by a low current for a short time during which the diode voltage is measured. This enables the isolation diode junction temperature to be calculated, and hence the chip temperature. Measurement of case temperature enables the calculation of thermal resistance. A silicon chip is basically a P type substrate with an epitaxial layer grown onto the P surface. The epi layer is a lightly doped N type structure (Fig. 1). Under normal modes of operation this P-N structure is reverse biased to isolate the transistors and resistors to enable correct circuit function.

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Thermal Measurement on Silicon Chip

All silicon chips have a PN diode structure for isolation.

Firstly, a large current is passed through this isolation diode to heat the chip, followed by a low current for a short time during which the diode voltage is measured. This enables the isolation diode junction temperature to be calculated, and hence the chip temperature. Measurement of case temperature enables the calculation of thermal resistance. A silicon chip is basically a P type substrate with an epitaxial layer grown onto the P surface. The epi layer is a lightly doped N type structure (Fig. 1). Under normal modes of operation this P-N structure is reverse biased to isolate the transistors and resistors to enable correct circuit function.

However, if the P-N junction is forward biased, then a diode with some series resistance exists, typically 5-15 ohms depending on the physical size of the chip. This isolation diode is available via the power supply connections. The silicon chip is first heated in an oven at two temperatures (say 250OEC + 100OEC) to calibrate the voltage drop of the isolation diode for a particular current I2. This voltage varies with temperature linearly (mV/OEC is constant), as shown by Fig. 2, and is a standard technique. The thermal measurement is then performed as follows: 1. Apply a large current I1 (typically 1 amp) to the forward biased isolation diode for a predetermined time

in order to heat the entire chip. Measure the voltage

V1 acr...