Microsystems and sensor networks

Lecturer - prof. Tadeusz Pisarkiewicz building C-1, room No. 316 e-mail: pisar@agh.edu.pl homepage: http://home.agh.edu.pl/~pisar

Assistants: Wojciech Maziarz, PhD , maziarz@agh.edu.plŁukasz Krzak, MSc, Eng, lkrzak@agh.edu.pl

Textbooks: 1. Nadim Maluf, Kirt Williams, An Introduction to Microelectromechanical Systems Engineering, Second Edition, Artech House 2004.2. Jacob Fraden, AIP Handbook of modern sensors: physics, design and applicattions, AIP New York, 1993.3. Waltenegus Dargie, Christian Poellabauer, Fundamentals of wireless sensor networks : theory and practice, Wiley 2010.

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Definitions of terms used

Sensor - a device that converts a quantity of one kind into a quantity of another kind (in most cases into an electrical signal)

Introduction

Lambda sensor for detection of oxygen in exhaust gases of a car

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Definitions of terms used, cont.

Microsensor - a sensor that has at least one physical dimension at the submillimetre level

The STJ-001 low-field magnetic microsensor in a die form, with activearea of 1 x 2 microns.

The die is 1.9 mm square and 300 microns thick. It has four gold wirebonding pads which allow four-point measurement of the device resistance. The field sensitivity of the STJ-001 is 5 nT, which is ten thousand times smaller than the magnetic field of the Earth.

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Definitions of terms used, cont.

Actuator - a device that converts an electrical signal into a nonelectrical quantity

Electrostatic actuators with applied voltage V which results in an attractive force:

(a) parallel plate actuator with force normal to the plate surfaces (b) electrostatic comb actuator with attractive force in the direction of

the interdigitated teeth.

5Examples of MEMS accelerometers: Analog Devices ADXL250 (on the left)and Motorola dual-structure microsystem before encapsulation (on the right)

Definitions of terms used, cont.

MEMS device – Micro-Electro-Mechanical System consisting of microsensors, actuators and microelectronic circuitry

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1. Evolution of microsensors

The vast increase in microelectronics technology has caused that the price-to-performance ratio of both sensors and actuators had fallen remarkablybehind processors. Consequently, measurement systems tended to be large and, more importantly, expensive. Work therefore started to use the microelectronic technologies to make silicon-based sensors, the so-called microsensors.

World market for ICs and microsensors from 1990 to 2000

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It is evident that the market for microsensors lags well behind the market for ICs. The main cause has been the relatively stable price-performance (p/p) ratio of sensors and actuators since 1960, as illustrated in the Figure below.

Price-performance indicators for ICs, sensors, and actuators

This contrasts markedly with the p/p ratio of ICs, which has fallen enormouslybetween 1960 and 2000 and is now significantly below that for sensors and actuators. As a consequence of these changes, the cost of a measurement system is, in general, dominated first by the cost of the microactuator and second by the cost of the microsensor.

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2. Evolution of MEMS

The miniaturisation of a sensor leads to producing of a microsensor, secondly the integration of a microsensor and its microelectronic circuitry gives so-called smart sensor; and thirdly, the integration of a microsensor, a microactuator, and their microelectronic circuitry produces a microsystem.

Many of the microsystems being fabricated today employ silicon microtechnology and this technology is commonly referred to as MST (microsystem technology).

Work to achieve this goal started in the late 1980s, and there has been enormous effort to fabricate microelectromechanical systems (MEMS) using MST.

Elements of a MEMS chip together with overview of its technology and applications

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3. Emergence of micromachines

Natural evolution will then lead to MEMS devices that move around by themselves.Such chips are commonly referred to as micromachines: microplanes, microrobots, microcars, microsubmarines. Micromachines, if developed, will need sophisticated microsensors so that they can determine their location and orientation in space and proximity to other objects.

Dimensions of microsensors, MEMS, and micromachines; they are compared with some everyday objects. The horizontal axis has a logarithmic scale.

They should also be able to communicate with a remote operator and hence will require a wireless communication link - especially if they are asked to enter the human body.

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