6 research outputs found
Test Structures for the Characterisation of Conductive Carbon Produced from Photoresist
Conductive carbon films are highly attractive for use as electrodes in electrochemistry and biosensing applications. Patterned photoresist films can be transformed into carbon electrodes using standard photolithographic techniques followed by pyrolysation of the photoresist in a furnace under a reducing atmosphere. Previous studies have been made of the electrical properties of blanket carbon films created using this method of fabrication. However, there is a need to investigate pattern dependent effects, particularly the extent to which the dimensions of the patterned films shrink during the high temperature processing. This study applies microfabricated test structures to the process characterisation of conductive carbon produced from standard positive photoresists
Development of a high temperature sensor suitable for post-processed integration with electronics
Integration of sensors and silicon-based electronics for harsh environment
applications is driven by the automotive industry and the maturity of semiconductor
processes that allow embedding sensitive elements onto the same chip without
sacrificing the performance and integrity of the electronics. Sensor devices post-processed
on top of electronics by surface micromachining allow the addition of
extra functionality to the fabricated ICs and creating a sensor system without
significant compromise of performance. Smart sensors comprised of sensing
structures integrated with silicon carbide-based electronics are receiving attention
from more industries, such as aerospace, defense and energy, due to their ability to
operate in very demanding conditions.
This thesis describes the design and implementation of a novel, integrated thin
film temperature sensor that uses a half-bridge arrangement to measure thin film
platinum sensitive elements. Processes have been developed to fabricate temperature
insensitive thin film tantalum nitride resistors which can be combined with the
platinum elements to form the temperature transducing bridge. This circuit was
designed to be integrated with an existing silicon carbide-based instrumentation
amplifier by post-CMOS processing and to be initially connected to the bond pads of
the amplifier input and output ports. Thin films fabricated using the developed TaN
and Pt processes have been characterized using resistive test structures and
crystallographic measurements of blanket thin film layer samples, and the
relationship between the measurement results obtained has been analyzed.
An initial demonstration of temperature sensing was performed using tantalum
nitride and platinum thin film resistor element chips which were fabricated on
passivated silicon substrates and bonded into high temperature packages. The bridge
circuit was implemented by external connections through a printed circuit board and
the bridge output was connected to a discrete instrumentation amplifier to mimic the
integrated amplifier. The temperature response of the circuit measured at the output
of the amplifier was found to have sensitivity of 844 μV·°C–1 over the temperature
range of 25 to 100 °C.
Two integrated microfabrication process flows were evaluated in this work. The
initial process provided a very low yield for contact resistance structures between
TaN and Pt layers, which highlighted problems with the thin film platinum
deposition process. Multiple improvement options have been identified among which
removal of the dielectric layer separating TaN and Pt layers and thicker Pt film were
considered and a redesign of both layout and the process flow has resulted in
improved yield of platinum features produced directly on top of TaN features.
Temperature sensitivity of the integrated sensor devices was found to depend
significantly on parasitic elements produced by thin film platinum step coverage, the
values of which were measured by a set of resistive test structures. A new
microfabrication design has enabled the production of a group of integrated
temperature sensors that had a sensitivity of 150.84 μV·°C–1 in the temperature range
between 25 and 200 °C on one of the fabricated wafers while the best fabricated
batch of sensors had a sensitivity of 1079.2 μV·°C–1