This stage is a sub-system of the micro drop tower for the Portela Research Group at MIT. Its purpose is to move samples to very precise locations under the drop mass. The samples are only 100-250 microns wide, so the stage has to position them with very high precision.
I designed the stage around three requirements:
- XY adjustment to position the sample under the drop mass.
- Tilt adjustment to level the sample and the stage.
- High precision to place samples within microns of accuracy.
Stepper motors drive each axis through a lead-screw design. The screw has a 1 mm pitch, so one full rotation moves the stage 1 mm. Each full step of the motor turns the screw 1.8°, which moves the stage 5 µm. The full range of motion is just under 40mm, which provides plenty of freedom for samples on 10mm-wide silicon wafers. The stage sits on linear rails to maintain its alignment as it moves in X and Y directions.
Five microns is already small, but I wanted to go further to allow room for the variety of need from different users. Micro-stepping lets the stepper driver move the motor in fractions of a full step, which brings the stage’s movement down to well under a micron:
| Step size | 1 | 1/8 | 1/16 | 1/32 | 1/64 |
|---|---|---|---|---|---|
| Calc. Move (µm) | 5 | 0.625 | 0.313 | 0.156 | 0.078 |
The user picks the step size with the sensitivity dial on the drop tower controller PCB, which is another sub-system that I designed for the micro drop tower project.
Sometimes, the samples that are being positioned are created with a slight tilt or the silicon wafers are glued to their stand at an angle. The stage allows for tilt correct with tree bolts mounted on springs support the stage. Tilting and rotating the whole stage is done by simply adjusting each bolt.
