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Indian Journal of Pure & Applied Physics (IJPAP) >
IJPAP Vol.50 [2012] >
IJPAP Vol.50(03) [March 2012] >
| Title: | Fabrication of ISFET microsensor by diffusion-based Al gate NMOS process and determination of its pH sensitivity from transfer characteristics |
| Authors: | Khanna, V K |
| Keywords: | Chemical Sensor
Ion Sensor
pH sensor
ChemFET
ISFET
Analytical Device |
| Issue Date: | Mar-2012 |
| Publisher: | NISCAIR-CSIR, India |
| Abstract: | The present paper describes the fabrication of ISFET (Ion-Sensitive Field-Effect
Transistor) by a four-mask, thermal diffusion-based process. The sequence of
physical and chemical processes for ISFET fabrication has been elaborated. In
the first photomasking step, the regions for source and drain diffusion have
been opened. The second photolithography defined the gate area. In the third
photolithographic step, contact windows have been opened, and in the fourth
photolithographic step, the metal pattern has been delineated. After completion
of the fabrication process, the wafer has been diced into chips, which have
been mounted on ceramic substrates to provide electrical connections for
source, drain and substrate. Except for the gate region, the whole chip and
wire bonds have been protected with insulating epoxy. For process
characterization, current-voltage characteristics of MOSFET test devices
simultaneously fabricated on the same wafer have been measured for gate-source
voltages from –5 to +5 V. These were found to be N-channel, depletion-mode devices indicating similar behaviour for
ISFETs. The pH-response of ISFET has
been evaluated by drawing its IDS-VGS characteristics after
immersion in standard buffer solutions and applying the gate-source voltage
through Ag/AgCl reference electrode. From these transfer characteristics, pH-sensitivity of ISFET has been
determined by finding the gate-source voltage necessary to ensure constant IDS, VDS condition. Technological shortcomings of this work
have also been pointed out, and necessary remedial measures have been
suggested. |
| Page(s): | 199-207 |
| CC License: |  CC Attribution-Noncommercial-No Derivative Works 2.5 India |
| ISSN: | 0975-1041 (Online); 0019-5596 (Print) |
| Source: | IJPAP Vol.50(03) [March 2012]
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