Think Outside the Chip: MEMS-Based Systems Solutions

MEMS is an acronym for Microelectro mechanical Systems; however, most MEMS implementations to date have not been systems at all, but rather devices. This article reports the constituents and some applications of what is defined as MEMS-based systems solutions, or MBSS. In Europe, this concept is commonly referred to as ”Smart Systems In tegration.” These MBSS use front-end MEMS devices — either one or a combination of many sensors, actuators, and/or structures — that work in conjunction with several other devices including signal conditioning commonly using application specific integrated circuits (ASICs), digital signal processing (DSP) with embedded microcontrollers and software, energy creation and storage, and networking communications functions.

All of these functions need to be interconnected and contained in a small, robust, low-cost package that has the ability to be tested in a highthroughput fashion. The concepts of classical system engineering of bringing the design team together from day one; co-design principles and modeling that acknowledge the interaction of the MEMS, other electronics, and packaging; reliability analysis; and embracing design for manufacturing and test are the principles that drive this approach (Figure 1). All of this is driven by the specific application.

Approaches to MEMS-Based Systems Solutions

Market research by Roger Grace Associates on MBSS applications has established that they fall into two categories. Category one has an “enabling engine” that drives the solution. This concept is driven by MEMS technology that is the intellectual property of the creator of the solution. As an example, a high-sensitivity accelerometer created by HP is the enabler for a wireless autonomous sensor network for seismic oil and gas exploration applications1 as well as the hand-held Phazer Near Infrared (NIR) spectrometer from Thermo Fisher¹.

The other approach, “commoditized integration,” uses standard off-the-shelf MEMS devices in conjunction with ASICs/DSPs with proprietary application software and proprietary packaging to create a solution. Examples of this approach are Schrader Electronics1 in its automotive tire pressure monitoring systems automobiles using off-the-shelf pressure and motion sensors; Hillcrest Laboratories¹ and Movea1 in their human-machine interface devices for gesture recognition using MEMS accelerometers and gyros; and Body Media for their weight-control/calorie-counting, bicep-wearable Link and Core system using a purchased three-axis MEMS accelerometer with internally developed sensors including (non-MEMS) skin temperature, galvanic skin response, and heat flux.

The value added to these “commoditized” solutions is the developers’ in-depth knowledge of the application, including the data acquisition, storage, processing, and transmission requirements, and the ability to successfully accomplish intelligent systems integration and provide software programming specific to the application. All of this is neatly packaged in a low-cost and robust fashion.

Applications

The applications for MBSS are wide and varied, as mentioned above. Based on our market research, one of the more significant opportunities for MBSS are autonomous wireless sensor networks (WASN). Many applications are currently under development at research universities and laboratories worldwide. One of major investigation is the use of WASN in infrastructure monitoring. Applications include civil engineering structures including bridges, dams, and buildings, as well as for structural monitoring of ships’ hulls and aircraft structures. The University of Michigan’s Center for Wireless Integrated MicroSensors and Systems (WIMSS) is part of a team working on a National Institute of Standards and Technology (NIST) grant to instrument bridges with accelerometers and strain sensors, collect the data, and wirelessly send the data to a central data collection platform to monitor the bridge system dynamic response in real time and over time under traffic conditions1. Similar systems are being developed jointly by MEMSIC and the University of Illinois Urbana Champaign¹.