Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Physical stress responsive
Reexamination Certificate
2001-08-07
2003-10-14
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Physical stress responsive
C438S050000, C257S415000, C257S417000, C257S420000
Reexamination Certificate
active
06632698
ABSTRACT:
FIELD OF THE INVENTION
The invention claimed and disclosed herein pertains to Micro Electro Mechanical Systems (“MEMS”, MicroElectroMechanicalSystems or micro-electro-mechanical systems), and in particular to MEMS having stiffened beams (sometimes called flexures), and methods for stiffening beams in MEMS.
BACKGROUND OF THE INVENTION
The present invention is directed towards structures which are used to support suspended masses in MicroElectroMechanicalSystems (“MEMS”). MEMS, as the name suggests, are microelectromechanical systems that provide mechanical components and electrical components (collectively, microelectromechanical components, which make up microelectromechanical devices, or “MEMDs”) to produce a micromachine capable of controlling, or responding to, an environmental condition within the system. The mechanical components and electrical components in MEMS are typically dimensionally measured in microns (1×10
−6
meters). MEMS devices typically include microsensors to detect changes in the system's environment, an intelligent component (such as a control logic circuit) which makes decisions based on changes detected by the microsensors, and microactuators which the system uses to change its environment. Example MEMS devices include inkjet-printer cartridges, accelerometers that deploy airbags in automobiles, and inertial guidance systems. MEMS are typically fabricated from, or are fabricate on, a substrate, and are fabricated using known (as well as newly developed) technologies. One of the primary technologies used in the fabrication of MEMS are depositional and mask technologies which are applied to fabricate the MEMS much in the same manner that semiconductor devices such as microprocessors and memory devices are fabricated. MEMS fabrication techniques also include photoetching and/or micromachining to remove part of one or more of deposited layers to thus define one or more of the mechanical or electrical devices. Micromachining often is performed using a focused ion beam such as an eximer laser for small adjustments to prototypes.
Certain micromechanical and microelectromechanical devices (“MEMDs”) comprise masses or mass elements which define surfaces which are supported by a beam or a bridge. The beam or bridge acts as a flexible member allowing the mass element to move with respect to surrounding structures in the MEMS. Typically the mass element is supported by the beam or bridge such that it is free of contact with the surrounding elements of the MEMD. The mass element can be part of a microactuator or a microsensor, as well as a component in other types of MEMDs. For example, a microactuator can be configured to drive a resonant sensor to cause the sensor to oscillate at its resonant frequency. In other applications microactuators can be used to produce a mechanical output required for a particular microsystem. An example of this latter application is using a microactuator to move micromirrors to scan laser beams (as for example in laser printing). Accordingly, the mass element which is supported in a MEMS by a bridge or beam defines an “area of interest” which can support microsensor components or other components which comprise parts of a microactuator. Alternately, the mass element itself can have electrical properties, such as conductance, capacitance or resistance, and the mass element can thus itself be used as the active component in the MEMD.
In general, it is desirable that the beam or bridge used to support a mass element in a MEMS have sufficient structural strength that it can support the mass element above another surface, or between two other surfaces. Turning to
FIG. 1
, a plan view of a section of a MEMS
10
is depicted in a simplified sectional plan view. The section of the MEMS depicts a component of a microelectromechanical device
11
, which comprises a mass element
12
supported by a cantilevered beam section
20
. The MEMD component
11
is defined from the surrounding substrate
16
. This can be accomplished using photolithographic processes, for example, wherein the zone
18
between the device
11
and the rest of the substrate
16
is removed by etching or micromachining. The mass element
12
defines an area of interest
14
.
FIG. 1
(and the other figures discussed below) is not to scale, but is depicted so as to facilitate understanding of the prior art. The prior art beam section
20
is a solid beam from its first end
21
where it is connected to the substrate
16
, to the point of attachment
23
to the mass element
12
. The beam section of these MEMD components must be sufficiently rigid such that movement of the mass element
12
does not occur in a direction indicated by the arrow “X”, but rather occurs in a direction into and out of the plane of the sheet on which the figure is drawn. (A brief review of
FIG. 3
, which depicts a similar prior art device, shows that the mass element
12
is intended to move in the directions indicated by the arrow “Y”). If the beam section
20
(
FIG. 1
) is insufficiently stiff to resist bending on the beam in the “X” direction (FIG.
3
), then the mass element
12
can come into contact with the inner wall
28
(
FIG. 1
) of the substrate
16
. This can cause improper sensor readings, failure to actuate another device, or complete failure of the device
11
should the mass element
12
become stuck due to friction between the mass element
12
and the sidewall
28
. One method to provide sufficient rigidity in the “X” direction is to make the beam quite wide (i.e., a relatively large dimension in the “X” direction).
However, the beam section
20
must be sufficiently flexible to allow the mass element
12
to oscillate relatively freely into and out of the plane (“Y” of FIG.
3
). However, these two objectives—allowing flexibility in the “Y” direction while providing rigidity in the “X” direction—are at cross-purposes. One problem with increasing the width of the beam section
20
to provide rigidity in the “X” direction is that it increases the mass of the beam, thus requiring more power to cause the mass element
12
to move. Further, providing a massive beam requires that complex calculations be performed to calibrate a microsensor or a microactuator in which the device
11
is a component. If the mass of the beam
20
were sufficiently small, then it's mass could potentially be ignored when making these calculations, greatly simplifying the design task.
One prior art solution to this problem is depicted in FIG.
2
.
FIG. 2
depicts a partial plan view of a slightly modified micromechanical device
11
′ in a MEMS
10
′. The device
11
′ is in most respects same as the device
11
depicted in FIG.
1
. Like-numbered components between the devices
11
and
11
′ of respective
FIGS. 1 and 2
are essentially the same. However, the micromechanical device
11
′ of
FIG. 2
has a modified beam section
20
′. The beam section
20
′ comprises a first beam member
24
, and a second essentially parallel beam member
26
, thereby defining an opening
22
between the two beam members. Each beam member is defined by a thickness “T”. The micromechanical device
11
′ is further depicted in a side elevation sectional view in FIG.
4
.
FIG. 4
is provided to facilitate understanding of how the device
11
′ can operate, and depicts an example wherein the device
11
′ is a microsensor. The mass element
12
of the device
11
′ supports a material (such as an electromagnetic material)
32
and
34
on the respective upper and lower surfaces of the mass element
12
. Semiconductor material
36
and
38
is formed into the surrounding substrate
16
proximate to the respective upper and lower surface of the device mass element
12
. As the mass element
12
is oscillated in the “Y” direction, an electrical property (such as electrical current or voltage) can be induced or varied between the semiconductor surfaces
36
and
38
. This variance can be detected and measured. As an environmental condition (such a
Hewlett--Packard Development Company, L.P.
Malsawma Lex H.
Smith Matthew
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