Технические науки / 6. Электротехника и радиоэлектроника
Zharikova I. V.
Research Supervisor – Doctor of Engineering Nevliudov I. Sh.
Kharkov National
University of Radioelectronics, Ukraine
Microelectromechanical systems testing
challenges
Microelectromechanical systems
(MEMS) is the integration of mechanical elements, sensors, actuators, and
electronics on a common silicon substrate through microfabrication technology
[1]. MEMS promises to revolutionize nearly every product category by bringing
together silicon-based microelectronics with micromachining technology, making
possible the realization of complete systems-on-a-chip.
MEMS products are becoming increasingly common essential components of
modern engineering systems such as the airbag (or inertia) sensors in
automotive industry, surgical devices and implantable biosensors in medicine,
optical switches and RF waveguides in telecommunications, and the navigation,
safe and arm in aerospace applications [2]. The current and increasing
success of MEMS stems from its promise of better performance, low manufacturing
cost, miniaturization and its capacity for integration with electronic
circuits.
The cost of testing has become a major portion
of the total cost of an electronic product. MEMS devices necessitate special
considerations during fabrication processes such as handling, dicing, testing,
and packaging. Most research work in the MEMS area centers on design, technology, and
packaging problems and not testing.
Electrical tests are one of the most important
methods employed to characterize MEMS. Electrical testing of MEMS can take on
many different forms including wafer probing, electrical trimming, final test
at temperatures, engineering characterization, and reliability evaluations.
MEMS products are designed to perform a variety of functions of
electromechanical, chemical, optical, biological and thermohydraulic natures.
Mechanisms that cause failure of MEMS devices thus vary significantly from one
type to another. Test instrumentation
depends on the specific type of MEMS device and the desired performance
characteristics [3].
Creating
accurate fault models requires a complete knowledge of all the possible failure
mechanisms in MEMS. Fault models are assumptions about how physical defects
affect the behavior of the unit under test. In the case of MEMS, where physical
failure mechanisms are much more complex due to presence of mixed domains,
developing fault models becomes a difficult challenge.
Most of
the on-going research in MEMS fault modeling and simulation builds upon the
approaches used in analog fault modeling and simulation. However, a large
variety of physical, chemical and other effects complicate fault model
generation for MEMS, making a purely analog approach inadequate.
So the
test problem is complicated by systems that contain a large number and large
variety component or modules. Thus, MEMS inherently poses a new challenge to
the testing community due to its multi-domain operational characteristics.
The
testing problem associated with MEMS has created serious limitations to the
high-volume commercial production of microsystems.
The
main difficulties in MEMS testing are [3]:
-
accessibility, controllability
and observability. There is limited electrical access (I/O connections) to most MEMS-based devices.
This prevents internal nodes access which in turn makes controlling certain
internal parameters and observing test responses difficult;
-
diverse function. Different
modules within the microsystem (i. e. sensors, actuators, analog or digital
signal processing circuits) require completely new approaches to testing.
Unlike digital and analog circuits, there are no known fault models and test
algorithms designated especially for the microelectromechanical structures
found in microsystems;
-
interference. In highly
integrated microsystems, various sub-systems are in immediate proximity and
therefore, can adversely affect each other. For example, heat dissipation of a
digital signal processor may result in the thermal expansion of the
microstructure used in the sensor circuitry. Such a change in the sensor
geometry results in faulty sensor output;
-
test environment. A system under
test typically requires some form of initialization. This is inherently
difficult for systems with sensors and actuators where special environmental
conditions are required;
-
packaging influence. Packaging
of a high-density multi-module system can cause mechanical stress that may
change the MEMS functionality. For
example, in case of a bulk-micromachined pressure sensor, any stress developed
on the diaphragm due to packaging can create undesired voltage fluctuations at
the output;
-
complex failure mechanisms. A
comprehensive MEMS testing methodology requires a complete knowledge of all the
possible failure mechanisms.
Problems
such as damping, stiction,
cross-axis sensitivity, over-load protection and in-process survivability need
to be analyzed and understood. These effects are quite complex and difficult to
model accurately for test generation purposes.
The test
cost pressure is constantly present in any manufacturing operation and
efficiency in the overall test strategy can provide a positive impact on the
overall product revenue. At the same time most testing techniques are highly
design specific. As a result, they may work well with one design but not with
others. The success of any testing technique depends on the fault models
applied. A majority of MEMS devices are inherently mechanical in nature and
therefore require some special considerations during various manufacturing
stages and testing.
References:
1.
Невлюдов, И.
Ш. Микроэлектромеханические системы и нанотехнологии [Текст] / И. Ш. Невлюдов,
А. А. Андрусевич, В. А. Палагин. – Харьков : Коллегиум, 2007. - 268 с.
2. MEMS and MOEMS
Technology and Applications [Техt] / Editor P.
Rai-Choudhury. – Washington : SPIE Press Monograph, 2000. - 528 p.
3. Kolpekwar, A. Development of MEMS Testing
Methodology [Техt] / A. Kolpekwar, R. D. Blanton // Proceedings of IEEE
International Test Conference, nov. 1997. - Washington. - 1997. - PP. 923-931.