Enhancing lifetimes of thermally modulated active plasmonic sensors

Active plasmonic sensors are an intriguing method of enhancing the sensitivity of traditional plasmonic sensors. One method of introducing active control over surface plasmon excitation is Joule heating. Modulated Joule heating can be achieved by passing an alternating current through the sensor. The consequent heating causes changes to the conditions of surface plasmon excitation, localized to the temperature distribution, due to the temperature dependence of the structure's optical constants. However, the introduction of a current flow and resultant heating to such sensors will accelerate environmental degradation and electromigration, particularly in silver-based sensors. This Letter proposes and evaluates the addition of a simple, naturally oxidized aluminum capping layer to active plasmonic sensors to improve long-term chemical and electrical stability. Under continuous operation, the capping of thermally modulated structures has been shown to increase lifetime by more than a factor of five while having no appreciable adverse effects on the sensitivity of the sensor.