The Properties and Sensing Mechanism of PdNPs-decorated Silicon Nanobelt Devices for H2 Sensing at Room Temperature
This study reports the properties and the sensing mechanism of Pd nanoparticles (PdNPs) decorated n+/n-/n+ double-junction silicon nanobelt (SNB) device as hydrogen (H2) gas sensor. The SNB devices are prepared via CMOS process. Plasma-enhanced atomic layer deposition (PEALD) is adopted for PdNPs deposition as sensing material on the Al2O3 dielectric of SNB devices.PEALD of PdNPs provides high conformity and fine control of the particle size. The PdNPs-decorated SNB devices working at room temperature are characterizedat H2 concentration ranging from 10 to 1000 ppm. Instead of using the traditional steady-state response, the slope of response and the corresponding sensing mechanism are presented to estimate concentration and shorten the response time. More than 60 % improvement in response time has been achieved for 10 to 1000 ppm H2 detection. To reduce recovery time, device localized Joule heating (DLJH) with a bias of 11 V for 240 s is demonstrated to restore the device back to the baseline.At a bias of 1 V, H2 sensing at room temperature consumes only 68.39 μW.
The average atmospheric hydrogen (H2) concentration is about 530 ppb, and its atmospheric lifetime is 2 years . H2 is a renewable and clean energy. However, explosion will be caused by 4% leakage of H2 in air. Therefore, the detection of low H2 concentration leakage as an early alert is essential in the process of production, transportation and future energy usage. On the other hand, H2 in human breath is thought of as an important biomarker regarding the condition of the human digestive system . Human breath exhibiting a rise of H2 > 20 ppm by 90 min after uptake of lactulose is considered to be positive of small intestinal bacterial overgrowth (SIBO) .
Among various H2 detection techniques, despite of the selectivity problem and the need of an external heater, metal oxide semiconductor (MOS) gas sensors have been a promising one because of its low cost and similar fabrication process to that of MEMS/IC. However, MOS gas sensors usually work at a temperature higher than 250°C to obtain an accurate H2 detection. Consequently, the power consumption and the safety consideration at high working temperatures limit its applications -. PdNPs-decorated silicon field-effect devices working at subthreshold swing region via bottom-gate modulation have been demonstrated as H2 gas sensors with high sensitivity and low power consumption -. However, such issues as long response time and recovery time occurring when devices work at room temperature are still a main challenge for real deployment. Moreover, an external heater may be needed when target gas sensing requires a higher sensing temperature. In this study, PdNPs-decorated n+/n-/n+ double-junction SNB devices with extremely low-power are demonstrated for H2 detection at the concentration ranging from 10 to 1000 ppm at room temperature. To deal with long response time during the operation at room-temperature, the slope of response is investigated and the corresponding sensing mechanism is introduced to link the slope of response to the dynamic interaction between H2 and PdNPs. To reduce the recovery time, DLJH is introduced and demonstrated to accelerate the desorption of H2. As a result, the response time of 56 s and a recovery of 240 s for 1000 ppm H2 detection at the room temperature have been achieved.