Scientists at the Laboratoire de Physique des Interfaces et des Couches Minces, Ecole Polytechnique, and Thales Research and Technology (both in Palaiseau, France) are making multiwalled carbon-nanotube (CNT) based bolometers that are inkjet-printed on a flexible plastic substrate. The devices could someday become components in body-monitoring systems.
Conductive silver ink was used to print electrodes on a 110-μm-thick polyimide sheet, then CNTs suspended in a mixture of water and propanol were deposited in channel regions between the printed silver electrodes. The CNTs themselves were between 1 and 10 μm long with diameters of 10 to 20 nm; the electrode channel lengths varied between 50 and 1100 μm. The optimized sensor design had an area of about 104 μm2 that had a 1.4 kΩ resistance and withstood a 1 mA current, resulting in a responsivity of 1160 V/W. The response time of the device was about 1 s. One undesired side effect was a dependence of photoresponse on the relative humidity of the surrounding air; the researchers hope to reduce this effect. They also aim to decrease the response time by optimizing the thermal conductance of the heat sink and the heat capacity of the sensing element. Contact Costel-Sorin Cojocaru at [email protected].
