MEMS grating scanning response testing provides comprehensive evaluation of the dynamic behavior of MEMS grating scanners, covering resonant frequency, scan angle amplitude, frequency response bandwidth, hysteresis, and transient characteristics such as rise time and settling time. Using advanced optical lever detection, laser Doppler vibrometry, and high-speed photodetection, our laboratory delivers accurate and traceable measurement results that support design verification, process optimization, and quality control for LiDAR, AR display, and spectroscopy applications.
Technical Overview
MEMS grating scanners are micro-optical-electro-mechanical devices that steer light beams by rotating or translating a micro-fabricated diffraction grating or grating mirror. Driven by electrostatic, piezoelectric, electromagnetic, or electrothermal actuators, these devices achieve large optical scan angles within millimeter-scale footprints, making them core components in solid-state LiDAR, compact projection displays, and miniaturized spectrometers.
The scanning response defines how the mechanical deflection of the grating behaves as a function of the drive signal, including its frequency, voltage, waveform shape, and duty cycle. Accurate characterization of the scanning response is essential for verifying that a device meets its intended beam-steering specifications, for validating actuator and spring designs, and for ensuring stable operation under real-world thermal and vibrational conditions. Scanning response testing quantifies both the steady-state behavior, such as amplitude-versus-frequency curves and voltage-to-angle linearity, and the dynamic behavior, such as step response, settling time, overshoot, and cross-axis coupling in two-axis scanners.
- Static response: scan angle as a function of DC drive voltage or power
- Frequency response: amplitude and phase versus excitation frequency
- Transient response: rise time, fall time, overshoot, and settling time
- Linearity and hysteresis of the voltage-to-angle transfer function
- Stability: pointing repeatability, drift, and temperature dependence
Testing Samples
Wafer-Level and Bare-Die Grating Scanners
Unpackaged MEMS grating devices on whole wafers, wafer fragments, or singulated bare dies can be tested directly on probe stations equipped with optical access. Wafer-level testing enables rapid statistical screening of resonant frequency, scan amplitude, and actuation thresholds before dicing and packaging, significantly reducing the cost of identifying process outliers.
Packaged MEMS Scanning Modules
Devices assembled in TO-can, ceramic LCC, CQFP, or custom optical packages, with or without transparent lids or windows, are accepted for full characterization. Testing of packaged modules includes the influence of package-induced stress, vacuum or hermetic encapsulation on quality factor, and window transmission effects on the optical measurement path.
Resonant and Quasi-Static Scanning Devices
Both major scanner architectures are supported: resonant scanners that operate at the mechanical resonance of the grating suspension for high-frequency, sinusoidal deflection, and quasi-static (linear) scanners that follow arbitrary waveforms such as ramps and triangular profiles. One-axis and two-axis configurations, including gimbal-mounted and comb-drive coupled structures, can be evaluated.
Integrated Scanner Subsystems
Complete beam-steering subsystems combining the MEMS grating with driver ASICs, closed-loop position sensing, optics, and control firmware can be tested at the module level. In these cases, the electrical drive signals generated by the on-board electronics are characterized together with the resulting optical scan response.
Testing Items
The standard scanning response test portfolio covers the key static, dynamic, and environmental parameters that determine beam-steering performance:
- Static scan angle versus drive voltage or drive power (DC transfer curve)
- Resonant frequency of each scan axis, with frequency resolution down to 0.1 Hz
- Frequency response curve: amplitude and phase versus frequency, including 3 dB bandwidth for quasi-static scanners
- Mechanical and optical scan angle at specified drive conditions, typically from 0.01 degrees to 60 degrees optical
- Quality factor Q derived from the resonance peak shape or ring-down decay
- Hysteresis loop area and width between forward and reverse voltage sweeps
- Linearity error and nonlinearity of the voltage-to-angle transfer function
- Rise time, fall time, overshoot, and settling time for step and triangular waveforms
- Pointing repeatability, angular drift, and long-term stability of the scan amplitude
- Cross-axis coupling and wobble between the fast and slow axes of 2D scanners
- Temperature dependence of resonant frequency, scan angle, and response bandwidth from -40 to +125 degrees Celsius
- Vibration and shock sensitivity of the scanning response for automotive-grade qualification
Testing Methods
Optical Lever with Position-Sensitive Detector
A collimated laser beam is directed onto the moving grating surface, and the reflected or first-order diffracted beam is projected onto a position-sensitive detector or a linear photodiode array. The spot displacement is directly proportional to twice the mechanical tilt angle, providing a non-contact, high-resolution measurement of the scan angle. This method is the workhorse for static transfer curves, hysteresis characterization, and amplitude monitoring at repetition rates up to several hundred kilohertz.
Laser Doppler Vibrometry
A laser Doppler vibrometer measures the instantaneous velocity and displacement of the grating surface with nanometer-scale resolution and megahertz bandwidth. LDV is used to extract the full frequency response function, identify higher-order vibration modes, quantify in-plane versus out-of-plane motion components, and measure ring-down decay for quality factor extraction without loading the structure.
High-Speed Photodiode and Knife-Edge Techniques
For resonant scanners at high frequency, a fixed knife edge or slit placed in the scanned beam together with a fast photodiode and oscilloscope converts the optical sweep into a time-domain pulse train. The scan angle is calculated from the known slit geometry and pulse timing, achieving sub-microsecond temporal resolution suitable for rise time, settling time, and overshoot measurements on fast axes.
Swept-Sine Frequency Response and Transient Capture
An automated test platform combines a waveform generator, low-noise bias and drive amplifiers, lock-in detection, and data acquisition to perform swept-sine frequency response measurements and to capture transient responses to programmed step, ramp, and burst stimuli. Closed-loop control of the drive amplitude maintains constant voltage or constant power conditions, and stroboscopic illumination synchronized to the drive signal freezes the grating motion for direct imaging of the deflected spot pattern.
Applications
MEMS grating scanning response testing serves every industry in which micro beam steering determines system performance:
- Automotive solid-state LiDAR: verification of scan angle, field of view, resonant frequency stability, and temperature drift for long-range perception systems
- Augmented and virtual reality displays: characterization of raster scan linearity, jitter, and settling behavior for high-resolution near-eye projection
- Compact projectors and pico-projectors: qualification of two-axis scanning response and color-sequential synchronization
- Raman, infrared, and hyperspectral spectroscopy: validation of grating scan calibration and wavelength repeatability
- Optical coherence tomography and medical imaging: confirmation of high-speed axial scanning response and duty cycle
- Barcode and 2D code readers: testing of scan pattern geometry, sweep rate, and pointing repeatability
- Laser marking and printing: optimization of scan linearity and bidirectional accuracy
- Optical communication and switching: evaluation of fast angular response and long-term pointing stability
- Research and development: feedback for actuator design, suspension spring optimization, and fabrication process control
FAQ
What scan angle range and frequency range can be measured?
Optical scan angles from approximately 0.01 degrees up to 60 degrees or more can be measured depending on the optical configuration, and resonant frequencies from tens of hertz up to several hundred kilohertz are supported. Angular resolution is typically better than 0.001 degrees with the optical lever method.
Can both resonant and quasi-static scanning modes be characterized?
Yes. Resonant scanners are characterized with swept-sine and ring-down techniques to extract resonant frequency, Q factor, and amplitude at resonance. Quasi-static scanners are characterized with DC transfer curves, arbitrary waveform tracking, and step response analysis to determine bandwidth, linearity, and settling behavior.
What sample forms and package types are accepted?
We accept whole wafers, wafer fragments, bare dies, and packaged modules in TO-can, ceramic, LCC, CQFP, and custom optical packages, with or without lids and windows. Electrically driven samples with standard pad layouts can be probed directly, while fully integrated subsystems can be exercised through their own driver electronics.
How is resonant frequency determined accurately?
Resonant frequency is identified from the peak of the amplitude frequency response curve obtained by a high-resolution frequency sweep with lock-in detection, and it can be cross-verified by FFT analysis of the free ring-down signal. For two-axis devices, each axis is measured independently while monitoring cross-axis coupling.
Is temperature-dependent response testing available?
Yes. Devices can be characterized inside environmental chambers over the range of -40 to +125 degrees Celsius to quantify the temperature coefficients of resonant frequency, scan angle, and threshold voltage, which is critical for automotive and industrial qualification.
What deliverables are provided after testing?
Deliverables include a formal test report with raw and processed data, static transfer and frequency response curves, transient waveform captures, extracted parameters such as resonant frequency, Q, bandwidth, linearity error, rise and settling times, and pass or fail judgment against your specified acceptance criteria.