Sensor technology 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.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. 1

Introduction 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) Lambda sensor for detection of oxygen in exhaust gases of a car 2

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 active area 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. 3

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. 4

Definitions of terms used, cont. MEMS device – Micro-Electro-Mechanical System consisting of microsensors, actuators and microelectronic circuitry Examples of MEMS accelerometers: Analog Devices ADXL250 (on the left) and Motorola dual-structure microsystem before encapsulation (on the right) 5

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 remarkably behind 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 6

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. This contrasts markedly with the p/p ratio of ICs, which has fallen enormously between 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. Price-performance indicators for ICs, sensors, and actuators 7

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 8

Monolithic integration Integration of MEMS accelerometer with (BI)CMOS 9

Sensors, in general, are used in many parts of an aircraft such as for measurement of altitude, direction of navigation, speed, cabin pressure and temperature, fuel quantity as well as for engine and hydraulic management and control. The low cost, low power consumption and the capability of electronic integration of MEMS sensors makes them suitable for distributed measurement which enables more accurate maintenance and control. Of the market segments discussed above, the IT peripheral segment is by far the largest (see next figure.) and consumer electronics the fastest growing. MST market per segment according to the NEXUS Market Analysis for MEMS and Microsystems III 2005–2009. 10

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. 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. Dimensions of microsensors, MEMS, and micromachines; they are compared with some everyday objects. The horizontal axis has a logarithmic scale. 11

Expansion of sensor application area. 12