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Temperature error in ºC -->
φETF (degrees)
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
100
95
90
85
80
75
70
65
60
-60 -40 -20 0 20 40 60 80 100 120 140
Temperature (°C)
Figure 7: Measured phase shift as a function of temperature.
Figure 8: Chip photo of one of the proof-of-concept devices.
-1
-60 -40 -20 0 20 40 60 80 100 120 140
Temperature in ºC -->
Figure 9: Temperature error over temperature for 16 devices; the black lines
indicate 3σ limits.
CONCLUSIONS
This paper has presented an overview of recently
developed integrated temperature sensors based on thermal
diffusivity. The thermal diffusivity of bulk silicon is a welldefined
function of temperature, and as such can be used to
create accurate temperature sensors. An Electrothermal Filter
(ETF) can be used to realize a temperature-dependent
7-9 October 2009, Leuven, Belgium
thermal delay, which can then be measured in various ways.
Proof-of-concept devices, realized in 0.7μm CMOS
technology, provide either a frequency or a digital output
that is a function of temperature. Without trimming, the
measured device-to-device spread is ±0.6°C (3σ) over the
military temperature range (-55°C to 125°C). This error is
dominated by lithographic inaccuracy, and is expected to be
much less in nanometer CMOS technology, as higher
lithographic resolution will reduce the device-to-device
variations in the thermal delay. Therefore, thermal
diffusivity sensors are well-positioned as temperature
sensors for thermal management in large ASICs and
microprocessors.
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©EDA Publishing/THERMINIC 2009 143
ISBN: 978-2-35500-010-2