Page 265 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

RADIATION SENSORS 245

Table 8.3 Some commercial radiation microsensors and their typical characteristics
Device Peak Supplier/ Size/ Typical Typical Price
a
wavelength Part Package output rise/fall (euro )
time
Photoconductive:
CdS Visible NORP12 15 mm 1 MQ to 100 fl 18 ms/ 2.4
(0.53 urn) plastic for 0.1 to 120 ms
10 000 Lux
Photovoltaic:
p-n diode Visible IPL1002 TO- 18 metal 0.01 to 250 ns 5.4
(0.75 jrni) 0BW can 100 mW/cm 2
PIN diode Visible Siemens TO-92 0.5 mW/cm 2 20 ns 1.8
(0.85 urn) SFH206 plastic
2
Diode & amp. Vis-NIR OSI5K TO-5 metal 30 mV/uW/cm 40 us/ 30.2
(0.90 jim) can 40 |is
n-p-n NIR Siemens 3 mm 50 uW/cm2 8 us/ 8 us 1.0
phototransistor (0.86 jim) SFH 309 plastic
Pyroelectric:
LiTaOS IR (7 to Sentel DP- 5 mm metal 1800 V/W 100 ms 8.0
15 ^m) 2101-101 case

"Note that 1 euro is worth approximately 1.1 US dollars here
a burglar alarm system. The use of a band-pass filter removes sensor drift caused by
changes in the ambient conditions.
Photoelectric and pyroelectric sensors are made using a relatively mature technology
and so there is a very wide variety of commercially available devices based on different
semiconductor materials, processes, and packages. Table 8.3 gives our choice of the
discrete devices that are commercially available together with their typical characteristics.
The prices shown are based on a one-off price for 1999 and depend on the choice of
package (e.g. metal can versus plastic package). The rise times are often a function of
radiation intensity, with higher levels producing faster responses.
Figure 8.17 shows a photograph of three different radiation microsensors: a CdS photo-
conductive sensor (NORP12) that has a relatively large active area of 12 mm 2 and a slow
response time; a p-n photodiode (OSI5K) with an active area of 5 mm 2 and an integrated
operational amplifier, and a pyroelectric sensor.
Radiation microsensors, together with temperature ICs, are a relatively mature tech-
nology and, therefore, can be readily employed within an integrated optoelectronic system.
In fact, the technology has advanced to such an extent that arrays of photovoltaic sensors
can be fabricated with associated electronics to make digital line-scan and array cameras.
These devices may be regarded here as smart microsensors because they usually have
integrated digital read-out electronics.

8.3.4 Microantenna

Finally, microwave or short-wavelength radio waves can be detected using a small metal
strip patterned using UV lithography onto a planar surface. The miniature antenna can