Thin-film aerogel thermal conductivity measurements via 3ω

Microhotplates for low power, and ultra dense gaseous sensor arrays using recessed silica aerogel for heat insulation

“…However, processing a thick layer of aerogel of 5 µm or more is extremely difficult using multilayer processing since the spin coating of aerogel is limited to 0.6 to 3 µm per layer [20]- [22]. In view of the fact that a relatively thick layer of aerogel is required for ultra low power MOX sensors, the step coverage problem for the metal interconnection lines between the sensor array and the CMOS chip circuitry will pose significant yield problem.…”

Improving Insulation Methods in New and Existing Fabrication Processes

“…Aerogels are created by forming a gel, usually out of silicon dioxide, and removing the water within it while preventing the structure of the gel from collapsing in order to create a micro-porous material that can be composed of up to 99% air with a low density and high surface area [19,20]. Originally developed by Kistler and Caldwell in 1931 [21] and first used as thin films by Prikash, Brinker, and Hurd in 1991 [22], the concept to use thin film aerogels as insulators for MEMS devices was first proposed by Honeywell International who approached Pam Norris about the idea and was supported through a DARPA seedling grant in collaboration between her Mechanical Engineering group at UVA for aerogel creation and device testing, the UVML for microfabrication, and Honeywell who provided technical insight as well as performing their own separate microfabrication and testing.…”

“…Minimizing the number of support pillars is desirable, but this limits the size of the device that can be supported by the nitride diaphragm to no larger than 1mm for acceptable operation since the larger the device, the more mechanical support the diaphragm needs and the more pillars that are required. More pillars reduces the benefits of suspending the device on such a membrane [19].…”

“…A surface aerogel thin film architecture could meet or exceed the performance of nitride diaphragms by providing a continuous film with the potential of a lower thermal conductance than nitride diaphragms [19], since bulk (not thin film) aerogel has been shown to have a thermal conductance that is an order of magnitude less than air [20]. Such a device would also have a more uniform temperature distribution, could support larger MEMS structures and could still be vacuum-sealed to prevent convection if needed.…”

“…Multiple aerogels samples were tested in the microfabrication process, each aerogel with different chemistries and drying methods [19]. A processing method for a testing structure could not be developed without having to submerge the sample in deionized water.…”