Invasive measurements of physical parameters in blood are very importa
nt for the intensive care. The integrated flow sensor presented here h
as been developed as a part of an 'intelligent catheter' for measuring
certain blood parameters. The sensor is based on the principle of hot
-film anemometry. The temperature difference on a chip is measured by
two diodes. One diode is heated by means of a polysilicon resistor in
close proximity. This diode is (for thermal insulation) placed on a 5
mum x 260 mum x 260 mum silicon membrane. For the membrane formation t
he implanted oxide layer of SIMOX substrates (Separation by Implanted
Oxygen) was used as a stop for backside etching. This technique allows
batch processing and is compatible with a standard CMOS process. In a
ddition, electronic CMOS devices can be mounted directly into the memb
rane. Switched capacitor circuits are used for sensor read-out electro
nics. The differential voltage at the diodes is amplified by means of
a two-stage operational amplifier with an overall amplification of 238
. The total chip size amounts to 1 mm x 5 mm. A change of flow velocit
y from 0 to 80 cm/s results in a change of the pulse width of 20 mus f
or a maximal chip temperature of 13 K relative to the ambient.