A thermal actuator typically has two anchor points to the substrate.
Many designs of thermal actuators have been used in MEMS
(we are not constrained to a hot/cold arm design),
with varying distances between the anchor points.

Take for example a rib actuator made of a metal,
which has a greater CTE than silicon.
As the ambient temperature increases, the ribs will expand more than
the silicon to which it is anchored,
and the center of the ribs will move to the side.
This won't happen with an all-silicon structure as the CTE is matched.

   --Kirt Williams, Ph.D.    consultant

----- Original Message -----
From: Jonathan Engel 
To: 
Sent: Monday, May 12, 2003 8:55 AM
Subject: [mems-talk] RE: Material for Thermal lateral actuator


> I am curious as to your thinking for #3.  How would the ambient temp
affect
> the actuator, be it metal or poly?  As far as I know the traditional hot
arm,
> cold arm lateral actuator is a single material, and would be unaffected by
> changes in ambient temp as long as they are slow enough to allow
equilibrium
> between the two arms.  From the small size of such structures this time is
> less than a second.  I would submit that you could substitute the word
> "aluminum" for your mentions of "Polysilicon" and "Poly" in #1 and #2
below.
> A disadvantage of Al would be the lower melting temp.
>
> My thought is that the main reason for using poly over metals is that
standard
> processes such as MUMPS for surface micromachining have made this type of
> structure easy to make, and the fabrication can be outsourced.
>
> -Jon
>
> >----- Forwarded Message -----
> >From: "Kirt & Erika Zipf-Williams" 
> >To: General MEMS discussion 
> >Subject: RE: [mems-talk] Materail for Thermal laternal actuator
> >
> >Here are some of the reasons:
> >
> >1. Polysilicon is process-compatible and has been available for a long
time.
> >2. Poly forms a protective oxide of limited thickness, preventing it from
> >"burning."
> >3. By using the same material (silicon) for the substrate and the
actuator,
> >the actuator is not unintentionally acutated as the ambient temperature
> >changes.
> >
> >    --Kirt Williams, Ph.D.    consultant
>
>
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