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  • Why is Low Frequency Noise Measurement for ICs Such a Big Deal?

    Even digital designers need to be aware of how noise impacts their circuits because most clocked designs today use a Phase Locked Loop (PLL) block which contains a circuit called a Voltage Controlled Oscillator (VCO) that is quite sensitive in operation to the effects of noise and process variation. As process node scaling continues the effects of low frequency noise increase. There are even new devices coming out of R&D like nano-wires, Silicon Carbide (SiC) and photonic devices where it's necessary to measure ultra-low current levels. During process development the engineers will need to accurately measure and characterize low frequency noise in devices so that designers of SRAMs, MEMs and sensors have the most accurate statistical models.

    Article: Jasper User Group-mos-noise-min.jpg
    Planar MOS device is sensitive to 1/f noise

    One of the newer vendors in the noise characterization space is Platform Design Automation which has created a fast and accurate system called the NC300.

    Article: Jasper User Group-nc300-min.jpg
    NC300

    Related blog - A Brief History of Platform Design Automation

    An ideal noise characterization system would have these characteristics:

    • Fast speed, seconds instead of minutes
    • Lowest current measurements, pA to nA
    • IC testing, SRAM testing, sensor noise testing


    How well does the NC300 compare to the ideals listed above?
    • About 8s to 10s per bias, up to 10X faster
    • Low noise floor of under 10-29A2/Hz
    • Current noise in the pA range
    • Integrated with Source Monitor Units (SMU) and Dynamic Signal Analyzer (DSA)
    • Supports both multi-die and multi-wafer measurements


    Article: Jasper User Group-system-noise-floor-min.jpg
    NC300 - system noise floor

    Other noise measurement systems can take weeks to measure 1/f noise with large samples to form corner or statistical models, but with the NC300 you're getting results 10X quicker than that. This is a big deal because time is money in the semiconductor business.

    With this type of instrumentation and software you can perform all four steps from noise measurement to circuit characterization for design engineers:

    Article: Jasper User Group-noise-flow-min.jpg

    The design of the NC300 includes the DSA and Low Noise Amplifier (LNA), saving you equipment space and the performance enables high-volume noise measurements, suitable for both on-wafer and packaged parts. With this kind of test and modeling setup you can characterize:

    • Random Telegraph Noise (RTN) in RRAM
    • Circuit noise test
    • MEMs sensor test
    • Mercury Cadmium Telluride (MCT) infrared device noise test
    • Use MeQLab software for data extraction and modeling


    Related blog - Are Your Transistor Models Good Enough?

    Noise Testing Examples
    Let's take a quick look at some specific noise testing cases starting with a type of low frequency noise called RTN where electrons or holes are getting trapped between the gate and well of devices which in turn causes vibrations in Vth values:

    Article: Jasper User Group-rtn-electrons-min.jpg
    RTN with electrons

    Article: Jasper User Group-rtn-holes-min.jpg
    RTN with holes

    Article: Jasper User Group-rtn-causing-multi-states-min.jpg
    RTN causing multi-states

    Circuit noise from an Op Amp can be measured and a statistical noise model automatically generated:

    Article: Jasper User Group-voltage-noise-density-min.jpg

    The IoT market is enabled by sensors, so here's a pressure sensor tested for both a low frequency spectrum and derived quality factor:

    Article: Jasper User Group-pressure-sensor-low-frequency-spectrum-min.jpg
    Pressure sensor - Low Frequency Spectrum

    Article: Jasper User Group-dervied-quality-factor-min.jpg
    Derived quality factor

    GUI
    A modern GUI makes learning and using the NC300 easy and intuitive:

    Article: Jasper User Group-gui-min.jpg

    Customers
    The NC300 has been adopted by leading foundries, design companies and research labs. The 5 leading foundries have benefited from NC300 with its fast speed and ease of use. Researchers are now able to do the noise measurement of super-low currents such as the dark current of photo diodes, which was never achieved with other systems.


    Summary
    There are multiple vendors offering noise characterization systems in the world, and the NC300 from PDA looks to be a strong, new player worth taking a look at.