Ultra-low power sensors
Small, low power sensors and actuators are vital for systems of all kinds to interact with their environment. Holst Centre and its partners are developing ultra low power (bio)chemical sensors, actuators and signal acquisition / conditioning ICs that can be implemented in standard CMOS processes.
The ultra-low power sensors program develops new sensor technology platforms that can be applied to a range of applications. It takes an innovative look at tried-and-trusted sensor approaches, reducing both size and power consumption. From these platforms, it creates sensors to meet specific application needs.
To achieve these size and power savings, the program brings together a wide range of expertise. In addition to designing new sensor concepts, this includes developing new materials and fabrication techniques.
The range of potential applications is vast. For example, systems for non-invasive monitoring of medical conditions and rapid point-of-care diagnostics could help bring healthcare into the home or to remote locations. Portable devices for measuring chemical markers in breath or bodily fluids like sweat are already attracting attention in the wellbeing and lifestyle domains. Meanwhile, new gas and vapor detectors could revolutionize air pollution monitoring and the ripening and storage of fruit.
Metal-oxide and GaN-AlGaN based sensors
The program is exploring several gas sensing device options based on ultra-thin metal-oxides and high electron mobility layers. For example, it has demonstrated a wireless system using GaN-AlGaN-based sensors that is capable of detecting NO2 in ambient air at concentrations down to 15 parts per billion (ppb), and metal-oxide FET that enables room temperature CO2 monitoring. Some of these highly sensitive sensor concepts can be made more selective by chemically modifying surfaces with self-assembled monolayers. The program has used this approach with a zinc-containing porphyrin to detect NO concentrations down to 100 ppb nitrogen gas, and dry and humid air.
Electrochemical sensors
Electrochemical sensors have great potential for detecting gases and ions in solution. The program has had great success in applying electrochemical sensors in body area network (BAN) applications. It has integrated a pH and Cl- sensor with a wireless node, demonstrating easy-to-use sweat analysis – potentially of great interest in areas as diverse as sport and care for the elderly. It has also created miniaturized impedimetric sensors for measuring cortisol – an important indicator in stress monitoring. Beyond BANs, the program has developed a compact sensor capable of detecting ethylene – a marker for fruit ripening – at concentrations around 100 ppb. This sensor has been fabricated on both glass and foil.
MEMS-based electronic nose
Compact, power-efficient devices capable of identifying complex volatile mixtures (“smells”) could open new applications in areas from quality control and wellbeing monitoring to safety and security. One way to do this is to collectively analyze signals from an array of high-sensitivity, partially selective receptors – essentially replicating the mammalian olfactory system within application-specific limitations.
MEMS resonators are well suited to this task, and the program has shown that microbridges with integrated transducers can be coated with absorbent polymers to detect volatile compounds at low concentrations. Further developments have led to a compact, low-power integrated read-out that enables high-accuracy, real-time frequency tracking. Moreover, by using different coatings on identical resonators, the program has demonstrated selective sensing of mixtures of compounds. Ongoing efforts to co-optimize the read-out and sensing elements, and to expand the library of functionalization layers should further accelerate the development of a miniaturized e-nose.