Tip Wear on the nGauge

 

We've been busy pushing the boundaries of CMOS-MEMS based AFMs in order to get ready for the launch of the nGauge. Our robust integrated thermal actuators allow for high speed, high precision scanning that can run for weeks, representing billions of cycles.

When it comes to tip wear, we’re predominantly asked these two questions:

  1. "What if the tip crashes or we break the device? How do we replace the tip?
  2. What if I regularly use the same device to image a sample? When I use a regular cantilever tip over 50 scans, the tip wears out and I can’t image anymore."
SEM image of the nGauge AFM Tip

SEM image of the nGauge AFM Tip

The nGauge uses integrated thermal MEMS actuators instead of large hysteresis-prone piezoelectric stacks to position the tip in all three axes. This enables precision positioning and very fast response times which helps to prevent unexpected mishaps. However, accidents may happen when handling tiny AFM probes, and the tips occasionally need to be replaced. Unlike conventional AFMs where you would replace only the tip when it breaks or wears out, single-chip AFMs are fully integrated but designed to be disposable. If the chip were to break, simply swap the AFM chip out for a new one. This means that every time you replace the chip you get a brand new tip as well as fresh scanners and sensors. As new breakthroughs in chip design occur, you will always be able to stay up to date with the latest improvements in tip shape, scan range, scanner linearity, and sensor performance.  

Tip wear over time is another concern, so we put together a weekend-long experiment to see how our tips would fare. Our sample was a 22 nm CMOS chip which had all the contact pads exposed. It has features that are about 200 nm wide and approximately 20 nm tall. We took 72 hours worth of images in the same 5 um x 5 um spot, using open loop lateral scanning. This is the culmination of over 700 images:

 

Things to notice:

  1. The quality of the tip does not diminish over time; the features stay constant throughout the 700 images. Our tip also does not apply any damaging forces to the sample. If you track one of the smaller fine-speckled particles, you'll see that it does not move over time; it doesn’t get pushed around.
  2. There are long 1 nm deep, 10 nm wide scratches underneath the contact pads all around the sample. These are visible throughout the entire video, and they do not change in size or shape.
  3. The image slowly shifts over time. Since our lab is located on the third floor of a fairly drafty building, the heat comes on pretty regularly. The minute changes in temperature and the resulting thermal expansion causes our sample to move around less than 1 um over the 72 hour period, without decreasing the quality of the image.

Throughout this experiment, the tip has tapped the sample over 2 billion times with no visible degradation in image quality. If you’re still curious about our lifetime scans, or want to suggest another experiment, you can contact us or join our mailing list.

 

As always, feel free to contact us with any questions!

 

 

 
ICSPI