The fabrication of a pH sensor which can be used in practical applications in biological and niedical fields was designed and manufactured using a new lance style ion sensitive field effect transistor. The lance can be used to measure pH levels in micro biological cultures without disruption of the culture and can be a powerful tool in real time Invitro medical diagnostics tool.
The reference electrode can be placed onto the chip by depositing a noble metal contact in the field region. This is referred as a Pseudo Reference Electrode, PRE. By bringing the PRE design closer to the membrane, the active test area for the ISFET will then be contained to the small perimeter of the gate. Also, with the PRE being very close to the gate membrane, a larger percentage of charged ions will interact with the membrane which can allow for a smaller gate membrane and still have strong sensitivity. The combination of these two benefits can create a very compact Perimeters PRE ISFET design.
With this compact design, it can be implemented on a MEMS cantilever for new testing methods in the medical and biological fields. By combining the ISFET device at the tip of a cantilever, the device can be put into use to test with minimum impact.
Deep silicon etching was attempted using a protective front side coat and a hot KOH bath to etch a patterned backside. Complications in preserving sensitive ISFET components needs to be resolved before completion of freestanding cantilever lance MEMS probe with ISFET sensor.
Sturdevant, Charles D.
"Biomedical Lance Ion Sensitive System,"
Journal of the Microelectronic Engineering Conference: Vol. 17
, Article 18.
Available at: http://scholarworks.rit.edu/ritamec/vol17/iss1/18