For efficient product development in micro- and nanotechnology

Efficiently measuring MEMS right on the wafer

Wafer-level testing prior to separating the chips allows the sorting out of bad dies early in the production process thus helping to keep MEMS production costs low while maintaining high yield and quality levels. While electrical test procedures are standard here, certain tasks are necessaryto verify directly the mechanical function, typically by optical measurement.

You can easily integrate Polytec’s measuring technology into virtually all commercially available wafer probes to do precisely that. By combining a (semi)-automatic probe station with a microscope-based scanning laser vibrometer such as the Polytec Micro System Analyzer, you can efficiently and quickly measure the dynamic behavior of MEMS right on the wafer. That way, you can achieve a high throughput and have a key tool for monitoring the production process.

Documents

Article better switching: characterization and optimization of BiCMOS-integrated RF-MEMS switches

Application note semiautomatic MEMS test

A practical example:

Time domain measurement of RF-MEMS switches on wafer level

MEMS prototype verification for process optimization

The development of a new microelectromechanical system (MEMS) always requires a new production process, unlike with pure semiconductor devices. Process recipes and modules have to be revised at the very least, since at present you still can’t fall back on standard recipes for new micromechanical components, as is otherwise customary in semiconductor development.

Both the system design and an optimized process design are essential if a structural element determined primarily by mechanical properties is to work properly. Prototype verification thus not only enables the design to be confirmed, but allows for affirmation of the manufacturing process too. To determine unexpected mechanical behaviour and model deviations, a powerful optical measurement by Laser Vibrometry is often the method of choice.

Due to its high frequency bandwidth, high lateral resolution and excellent amplitude resolution, a laser vibrometer from Polytec should be the first tool you reach for so that you can reliably determine modal properties of MEMS such as transfer functions, resonance frequencies, damping and deflection shapes. The topographical analysis is also important for component development and process optimization. Surface data such as step heights and other dimensions provide you with valuable information about current process parameters, so you can reliably control the MEMS component manufacturing process.

Documents

Article topography of 3-D surface micromachined microsensors

A practical example:

CMOS / MEMS co-integrated flow microsensor

The figure illustrates the a characterization of the Topography of a CMOS / MEMS co-integrated flow microsensor carried out using the surface topography option of the MSA-500 Micro System Analyzer from Polytec. The flow microsensor had been realized using silicon-on-insulator (SOI) technology.

(Copyright: Université catholique de Louvain, Belgien)

Characterizing ultrasonic transducers in real time

Ultrasonic transducers produced using microsystems technology are promising for medical ultrasonic applications. Here, you essentially make a distinction between so-called pMUTs and cMUTs (piezoelectric Micromachined Ultrasonic Transducers and capacitive Micromachined Ultrasonic Transducers respectively).

cMUTs have unique properties compared with conventional elements. Thanks to the membrane’s bending mode deflection shape, the transducer’s mechanical impedance reduces, while energy transfer to the ambient medium improves at the same time. Microfabrication also enables affordable series production of cMUTs using semiconductor technology. The semiconductor switching circuit can be directly integrated on the same chip, so as to simply create even large-sized 1D or more complicated 2D array configurations.

A combination of different methods is often used to characterize new ultrasonic transducers. Finite element simulations predict the transducer’s behaviour, taking the surrounding medium into consideration too. You can then measure new transducer prototypes with microscope-based laser vibrometers such as the Polytec MSA Micro System Analyzer, to directly determine the mechanical frequency response of the sound transducer surface. In doing so, you will come to appreciate the large frequency bandwidth and real time capability that you use to reliably and accurately measure transient processes in particular.

Documents

Article FEM simulation and measurement validation of an ultrasound transducer

Application note optimization of ultrasonic instruments

Application note surface vibration measurements in the ultra high frequency range

A practical example:

IMEC in Belgium characterized a unique cMUT with the Polytec MSA and, based on the results, determined the spatial pressure field in the transfer medium using the Rayleigh integral method. The results were subsequently confirmed with independent hydrophone measurements.

RMS displacement of single cMUT cell

Contactlessly characterizing SAWs

As surface acoustic wave (SAW) filters are electronic components that work through surface acoustic waves they are in fact mechanical filters. Due to their superior properties, they are an integral part of high-frequency applications such as mobile telephony. Optimization of the SAW surface’s micro-acoustic properties is one of the key tasks involved in developing new SAW components.

Due to the high frequencies, short acoustic path lengths and small vibration amplitudes, the measurement and visualization of surface waves places particular demands on measuring technology. Using a laser vibrometer is one of the few solutions available for measuring vibration on such systems.

Polytec’s laser Doppler vibrometers enable you to conduct non-contact characterization operations across all frequencies, even when faced with broadband excitation. The deflection shapes are visualized in an impressive way. You can even examine transients and relaxation behaviour. Key results are determining properties such as the filter characteristics and performance losses (leakage).

Documents

Article serving healthcare: using acoustic vibrations to manipulate liquids for handheld diagnostic devices

A practical example:

In addition to their use as electronic filters, SAWs play a key role in microfluidic applications too. In this regard, SAWs are used for targeted droplet manipulation of biomaterials. When such lab-on-a-chip components are being developed, the surface dynamics are examined with high-frequency vibrometers such as the Polytec UHF-120 due to the non-contact optical measurement, the frequency bandwidth and the high resolution.

116 MHz ODS of surface acoustic wave device

Conducting extensive and precise micromechanics analyses

The possibility to directly integrate microscopic, mechanical functional units with semiconductor electronics at silicon level gave rise to a multitude of different micromechanical sensors and actuators and to the huge success of MEMS and microstructures.

The sheer range of product types and areas of use is huge.

The variety of device type encompasses pressure and inertial sensor systems for automotive and aerospace applications, MEMS microphones, MEMS acceleration and gyroscope sensors for portable electronic devices, a wide range of micro mirror elements for light manipulation, energy harvesters for autonomous systems and microbalances for extremely small material quantities. And, lastly, there are pMUTs and cMUTs for generating ultrasonics in medical technology and micro-acoustic elements such as SAWs, which are increasingly being put to use as electronic filter elements, but are also deployed in lab-on-a-chip applications too.

Reliable and precise measurement of not only the electrical measuring technology, but also the direct mechanical function – in other words, the movement of the smallest silicon components – is absolutely essential to developing MEMS components such as this.

Using the microscope based single-point or scanning vibrometers from Polytec, you can measure displacements in the pm range, and acquire transfer functions and operational deflection shapes in either 1D or 3D, with a high frequency bandwidth and lateral resolution in the µm or sub-µm range. You also have the option of capturing your microsystem’s topography with the MSA Micro System Analyzer.

Documents

Article good vibrations: laser vibrometry and its role in micromechanical device development

Article better switching: characterization and optimization of BiCMOS-integrated RF-MEMS switches

A practical example:

The MSA-100-3D Micro System Analyzer allows for a real 3D vibration measurement with pm path resolution for both out-of-plane (OOP) and in-plane (IP) components. Here, this is taking place on an MEMS cantilever.

Testing the reliability and service life of MEMS

MEMS sensors and actuators are key functional elements in many devices and systems and, more and more often, they have safety-related functions too. Thus they have to be reliable and guaranteed throughout the system’s entire service life often under challenging operating conditions.

Therefore verification of new MEMS components has to take place under exactly these conditions. Vacuum or climatic test chambers are used to simulate the pressure loading or air humidity influences and stimuli like mechanical excitation or radiation are applied. The long time function stability is verified in accelerated aging tests.

Since, unlike conventional semiconductor elements, MEMS feature moving, micromechanical components as their key functional elements, the capability of measuring the dynamic, mechanical system behaviour is extremely important during reliability and service life tests.

Polytec’s Micro System Analyzer offers you all the relevant measuring modes for this purpose. The highly versatile measurement system can also be equipped with special lenses with large stand-off distancess to measure both static and dynamic component behavior from outside a test chamber.

Documents

Application note monitoring MEMS motion under vacuum

A practical example:

Vibration measurements on MEMS in a vacuum chamber

The influence of ambient pressure on an MEMS module’s dynamic properties is measured with the Polytec MSA, which is used either in conjunction with a vacuum chamber or in combination with a vacuum probe station for measurements at wafer level.

MEMS characterization for Biology and Medicine

MEMS and microstructures are key basic and cross-sectional technologies for an extremely wide range of medical and biological applications. The scope of use ranges from lab-on-a-chip applications with high-frequency surface waves for rapid medical diagnostics, to MEMS microphones for use in hearing aids, and ultrasonic transducers for medical imaging based on microsystems technology.

You can rely on the non-contact, microscope-based optical measuring technology from Polytec to determine the surface topography and dynamic properties of medical MEMS sensors and actuators. Microscope-based vibration measurement is also used in bionically inspired “technology transfer” from natural to technical systems to measure the biomechanics of insects’ hearing, for example.

Documents

Article vibration-based detection of biomolecules

Article serving healthcare: using acoustic vibrations to manipulate liquids for handheld diagnostic devices

A practical example:

Micromachined ultrasonic transducers (pMUTs & cMUTs) are pushing the boundaries of real-time 3D medical imaging (sonography) in applications such as IVUS (intravascular ultrasound) and echocardiography.

To characterize the micromechanics of these transducer elements, measurements must be performed at high frequencies (~10 MHz) and with a high spatial resolution (<1 μm). The various possibilities offered by Polytec’s Micro System Analyzer provide this information for pMUT and cMUT development with maximum precision and zero contact.

Deflection shape of cMUT transducer array (Univ. of Alberta)