[11a-S421-1~12] 3.9 Terahertz technologies

▲ [11a-S421-6] Effect of Joule Heating on Titanium Wires for Terahertz Antenna-Coupled Bolometer

〇(D)DURGADEVI ELAMARAN¹, KO AKIBA², HIROAKI SATOH³, NORIHISA HIROMOTO², HIROSHI INOKAWA³ (1.GSST, 2.GSIST, 3.RIE)

Keywords:Joule heating, Temperature coefficient of resistance, Antenna-coupled bolometer

For resistive bolometers, the important criterion is the temperature coefficient resistance (TCR) of thermistor material, since it is directly proportional to responsivity (R_v) and inversely proportional to the noise equivalent power (NEP). Especially, the device performances of metallic bolometer directly gets benefit from the improved TCR. The TCR of thin and narrow wires is affected by the presence of defects or grain boundaries, and can be increased by annealing. Therefore, this time we study the effect of Joule heating caused by the large current through the wire. Titanium has been selected as a possible candidate for thermistor material due to its large resistivity and small thermal conductance. The two devices with different lengths (L) 50 µm and 100 µm and same width (W) of 2 µm were taken for characterization. The basic parameters of device such as electrical resistance (R) and TCR were obtained by DC IV measurement at 240-300 K. The measured resistance (TCR) of devices are 252 Ω (0.202 %/K) and 495 Ω (0.204 %/K), for L = 50 µm and 100 µm, respectively. The electrical resistance linearly increases with the temperature. To check the effect of Joule heating large constant voltage instead of current was then applied step by step to avoid the thermal run away. Surprisingly, the reversal of the TCR value to negative one was observed as a result of Joule heating. The measured resistance after Joule heating are 499 Ω and 1.13 kΩ, for L = 50 µm and 100 µm, respectively, which is around 2 times larger than before Joule heating. The measured TCR value are -0.222%/K and -0.099 %/K, for L = 50 µm and 100 µm, respectively. The absolute value of TCR for the former becomes larger than that before Joule heating. Hence, the results implies that the Joule heating can improves the performance of the device by changing its material property.