Links

Overview

Detailed Equipment List

• Electronic Equipment

• Probe Station

• Image Data Acquisition

• Environmental

Equipment used to characterize MEMS devices at Sandia National Laboratories.

Overview

The purpose of this document is to review the equipment necessary to establish a MEMS characterization station and to give the user a starting point for establishing their own characterization equipment set.  Many of the links require an internet connection.

The specific equipment vendors listed are suggestions only and do not constitute an endorsement of the companies.  The products mentioned may be substituted with any other equivalent equipment.

Referring to the Detailed Equipment List; one can organize the overall characterization station into several equipment sub categories. 

• Electronic - required to drive the microsystem devices either packaged, in gel pack or at the wafer level.  This set of equipment includes function generators, signal amplifiers, oscilloscopes, and requisite cables.
• Probe Station - Microscope, platform, electrical probes required for both visual inspection and electro mechanical characterization of wafer and gel pack parts.  Packaged parts do not require probes, however, the microscope is needed for visual characterization.  The microscope also consists of several objectives and a white light illumination source.
• Image Data Acquisition - Required to document visual defects and part functionality.  This equipment set consists of video camera, video capture card/computer, associated software, video monitor, video recorder, strobe light source, and high speed camera.
• Environmental - In order to maintain a relatively clean micro environment, the characterization station needs to be placed either in a clean room or within a clean hood as shown in the photograph above.  If one is only going to characterize packaged parts (incorporating a clear window for viewing), then a clean environment is not necessary.  An example of this situation would be in a classroom environment.  For good viewing and image capture, having the probe station on a vibration isolation table is also a requirement.

Detailed Equipment List

Electronic

Function Generator

MEMS devices require a variety of driving waveforms.  An individual device (e.g., Microengine) may require up to 4 channels to drive plus ground.  Custom waveforms may be required for optimized performance.  In general, clipped square and sine functions are typical (0 to +100V).  To generate these signals, Sandia typically utilizes either a National Instruments AT-A0-6 High Performance Analog Output Board (installed in computer) or a stand alone (external) function generator such as the Agilent 33120A/33220A or Keithley Instruments 2400.  The Analog Output Card card requires specialty software such as Super µDriver^TM (Tegam Inc.), MEMScript^TM or LabView^TM.(National Instruments). 

Amplifier

Most function generator outputs are in the range of 0V to 10V (peak to peak).  Many of the MEMS devices utilize electrostatic actuation which require voltages on the order of 100V, hence, amplification is required.  If the devices being studied are low power and frequency (bandwidth), the an amplifier such as TEGAM's 2375 will suffice.  However if high frequency and or high power is required, Ktech's SNLKP24W  or Micro Tech Instruments' MTI24KP (both Sandia licensed designs) would be appropriate.  Higher power (200mA, ??V) is required for thermal actuators when compared to a TRA (Torsional Ratchet Actuator). 

Oscilloscope

It is good practice to use an oscilloscope (Agilent Technologies 54624A) during MEMS characterization.   This allows the tester to verify the signals being sent to the device and is useful for troubleshooting.

Dual In Line Package

In order to test packaged parts, a Dual In Line Package (DIP) is convenient means to make electrical connections to the components.  At Sandia National Laboratories Light Laboratory, the HP 16058-6007, HP 16147-6002 and HP 16058-60006 (Hewlet Packard 18, 24 and 28 pin DIPs, respectively) socket modules are utilized.  Agilent also provides a source for socket modules.

Probe Station

In order to test devices still on the wafer or individual die, a probe station is required.  For the purposes of this document, we define a probe station to consist of a microscope, probes, and platform (stage).  One may decide to assemble a probe station from separate components or purchase a complete setup.  The Alessi REL-6100 (Cascade Microtech) and the Signatone CAP-463 (Signatone) are two systems currently used at Sandia.

Micromanipulators and Probes

Sandia surface micromachined MEMS devices require two to five micromanipulators for actuation. Micromanipulators also referred to as micropositioners have three degrees of freedom (x,y and z) and are made to allow fine movement of the probe tips.  These are held to the platform either by vacuum (requires house vacuum or an additional pump) or magnetic force. Surface micromachined devices fabricated at Sandia typically require two to five probes two actuate; one can employ Alessi MH2 or the Signatone S-926 micropositioning probe.

Microscopehttp://www.cascademicrotech.com

The microscope should include objectives between 10X and 100X - a three objective turret is adequate.  Objectives should have a long working distance (~2-4cm) as to provide ample space for probes. In addition to the eyepieces for standard viewing, a camera mount is a requirement.  The ability to simultaneously view and record images is critical for efficient image analysis.  For MEMS inspection, illumination must be top down (many "standard" microscopes used in other applications illuminate from the bottom through the sample).  Dark field and brightfield illumination allow for enhanced visual inspection. The ability to switch between more than one light source is desired but not a strict requirement (CW or continuous wave illumination and a strobe source is very useful).  If interference microscopy is desired in order to include optical height and critical dimension measurements of MEMS physical structures, there are additional requirements.  Generally, such measurements are done on a separate system specifically designed for such an application. 

The ability for microscope head (consisting of the objectives, eyepieces and associated optics) to move independently of the stage is important.  This allows one to adjust the field of view while the electrical probes are making contact with the running device.

Light Sources

A standard white light source comes with most microscope systems (Halogen source from EKE from Micro-Tech).  A strobe light source with frequency and phase adjustment (relative to actuation waveform) is vital to observe high frequency actuation.  Sandia utilizes the Olympus ALS-12000S (Carsen Group). 

Image Data Acquisition

A Video camera mounted to the microscope provides a source to the image capture / video card in the computer as well as external video/DVD recording devices and viewing monitor.

When using the strobe in conjunction with the video/image capture tools, one can acquire detailed device position vs. time information.  This is done by adjusting the phase of the strobe relative to the drive signal.

While characterizing devices, we often measure the distance an actuator or shuttle travels.   We use systems that provide an overlay on a video monitor (Boeckler Instruments VIA-100) and systems that provide image capture with measurement capabilities (Visual Inspector Imaging Software from Cimarron Computer Engineering Inc.).

For extremely fast events, such as the sudden uncoiling of a spring, a high speed camera may also be utilized.  To see an example of what one can do with a high speed camera (3500 frames/sec), select either the 270 or 360 degree micro coiled spring video clip.

Environmental

Vibration Isolation

Vibration isolation will improve image quality, avoid damage from probe tip vibration.  There are several types of vibration isolation systems in use at Sandia.  Additional sources include Kinetic Systems and Technical Manufacturing Corporation.

Clean Benches - Vertical Laminar Flow

A clean area is required when probing non-packaged parts.  Vertical Laminar flow clean benches are adequate for probe stations - enough space should be afforded to be able to handle parts in the clean environment.  Electronic support equipment such as the computer, oscilloscope, amplifiers etc, do not have to be in the clean environment.  There are several levels of clean environments utilized at Sandia, including clean benches from Envirco.  Other sources include the Baker Company who offers a short Introduction to Clean Benches.  Terra Universal is another source for vertical laminar flow stations.  Tech Rite also is a Vertical Laminar Flow station as well as Portable Clean Room Kits. 

Characterization Technologists should wear clean room gloves and smocks when testing devices.  Hairnets and face masks ("beard bags") will also reduce the risk of particulate contamination of open parts.  Parts should always be handled within the laminar clean environment.  In addition, the proper grounding of equipment, probe station components and technologists will reduce the possibility of electrostatic discharge (ESD) damage to the micro devices.