Fabrication and Characterization of a Micro Turbine/Bearing Rig
Chuang-Chia Lin, Reza Ghodssi, Arturo A. Ayon, Dye-Zone Chen, Stuart Jacobson,
Kenneth Breuer, Alan H. Epstein and Martin A. Schmidt
Microsystems Technology Laboratories and Gas Turbine Lab
Massachusetts Institute of Technology, Cambridge, MA 02139, USA
This paper reports on a process to build, package,
and instrument a 5-level wafer-bonded micro-machined
The process flow involves the use of 5
wafers, 16 masks, and 9 deep silicon etching steps, as well as
utilizing aligned wafer bonding, double-sided deep reactive
ion etching (DRIE), and Laser-Assisted-Etching (LAE). This
paper also shows experimental results on flow characteristics
of the hydrostatic thrust bearings and the preliminary
rotational performance of the device.
The first major fabrication challenge of realizing a
miniature gas turbine generator is to demonstrate a baseline
process capable of integrating the turbine rotor, bearings,
and gas interconnects into a small package  .
structure, called the micro-bearing rig, not only validates a
process methodology for fabrication of freely-rotating high
aspect ratio devices, but it is also a vehicle for research into
critical micro air bearing stability issues.
An exploded view of the device is shown in figure
1. The turbine rotor, located in the 3
wafer, is supported by
two different air bearings. (Fig. 2)
Two pairs of wafers
which cap the center wafer from both sides provide the pair
of hydrostatic thrust bearing that support the rotor axially.
Each hydrostatic thrust bearing has eight flow restrictors that
provide the required pressure compensation. Externally
pressurized nitrogen is brought in through these restrictors
and flows through the bearing gap only a few microns wide.
A self-pressurized hydrodynamic journal bearing is designed
to support the bearing radially . Counter rotor-tilting flow
channels and fluidic interconnects are also incorporated into
the two wafer pairs that cap the center wafer.
To simplify the nomenclature, we named the wafers
in terms of functionality.
As shown in figure 1, from top to
bottom, they are called: forward foundation plate (FFP),
forward endplate (FEP), rotor plate (RP), aft endplate (AEP),
and aft foundation plate (AFP).
Exploded view of the micro bearing rig.
The five layers are: 1. Forward foundation plate
(FFP), 2. Forward endplate (FEP),
3. Rotor plate
(RP), 4. Aft endplate (AEP), and 5. Aft foundation
Schematic cross-sectional drawing
indicating the location of the bearings and the SEM
of the actual device cross-section.