**[Texas Tech University]{.underline}:**

**Design Description:** Our module contains 5 different MEMS devices.
These designs were done during the Spring 2005 semester at Texas Tech
University in the MEMS II/III class.

\(1\) The one we are entering into the design competition is labeled as
microAFM. It is essentially an X-Y stage, driven by two TRAs, that can
be used to position/scan a pseudo-AFM cantilever arm with a dimple at
the end used as the contact tip. The travel is 110 microns in X and Y.
The layout allows the arm to be extended off the edge of the chip to
access an external Z-stage where a sample could be placed. Due to TRA
limitations (i.e., uni-directional rotation), the arm cannot be
retracted at this juncture. The TRAs are used to drive a gear with a
spiral slot etched into it. A pin that is positioned in the slot is
connected to the X or Y stage and is pushed away from the center as the
gear turns. The long spiral path allows more precise control of the
stages movement. The AFM arm is connected to a central pin that is held
between the X and Y stages and is held above poly0. The pin joint cut
was used to minimize play in the pin to 200 nm in one axis. The other
axis is 1 micron. Once the pin is being pushed, the backlash should
disappear. A scale has been added to measure the distance traveled.
Guides and stops are included to constrain travel of the arms in the
specified direction. This design was done by Phillip Beverly, a senior
undergraduate Electrical Engineering student.

\(2\) smallTime is designed to be one of the world\'s smallest
mechanical clocks. A single TRA is geared down to run separate second,
minute and hour hands. Additional levels were added to gears in order to
change levels and to allow hands to be fabricated. This design was also
done by Phillip Beverly.

\(3\) microChain is an adaptation of a previous SUMMiT V chain with an
eye towards improving performance. One TRA is used to drive a linear
rack that is attached to a tensioner. The tensioner can freewheel after
tensioning allowing rotation of the chain. The linear rack was designed
using a similar slotting process used for the main pin in the microAFM.
A second TRA is used to drive the chain. Overhangs and guides are used
to keep the chain from releasing from the surface. This design was done
by Shad Holt, a graduate student in Electrical Engineering with
assistance from Phillip Beverly.

\(4\) Torsion micromirror is an array of electrostatically actuated
mirrors with 35 microns pitch. The long hinges are required to allow
torsional motion of the relatively stiff polySi. The same array is
printed twice.

Both actuation and sense electrodes are below each mirror. These mirrors
were partially simulated in ANSYS and functionality will be compared to
predicted results. A number of students designed and simulated these
mirrors.

\(5\) Piston micromirror is an array of 8 electrostatically mirrors with
some variations in hinge length and electrodes. Both actuation and sense
electrodes are below each mirror. These mirrors were partially simulated
in ANSYS and functionality will be compared to predicted results. A
number of students designed and simulated these mirrors.

**Comments on Usefulness of Design for Educational Demos:** We believe
all the devices have many educational uses. We have begun work on
preparing a journal article that will expound on the educational
benefits of the design exercise for our students. We would enjoy seeing
other groups and institutions learning something from actuating these
devices. Something as common as a clock will be useful for reaching
individuals with little prior exposure to micro devices.

**Comments on How Design Exploits Strengths of SUMMiT-V:** All 5 layers
of poly-silicon were used on a number of the devices. This allowed some
very complex mechanical systems to be realized. The pin joint cut was
used in its usual way for freeing up gear hubs as well as used to design
the pins for the microAFM and the linear rack for the microchain
tensioner.

Standard TRA\'s have been used to drive the devices. Dimples have been
utilized in the usual fashion to mitigate stiction as well as one
special one used as a pseudo-AFM tip. The mirrors illustrate that things
other than gears can also be readily fabricated in SUMMiT.

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