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DESCRIPTION JP2017525263
The present invention relates to one transducer element (1), which comprises one movable
membrane (2, 2a, 2b) with one edge (4) and the membrane (2, 2a, 2b) with one frame (5) to
which the edge (4) is fixed, and one reinforcement member (10), this reinforcement member
being one first part of the frame (5) , One second part of the frame (5) on the opposite side of the
first part is connected to each other. [Selected figure] Figure 1
Transducer element
[0001]
The invention relates to a converter element. The transducer element may in particular be a
transducer element configured to convert an acoustic signal or other pressure fluctuations into
an electrical signal. Such transducer elements are used in particular for condenser microphones.
[0002]
In condenser microphones, it is extremely important that the transducer elements be as compact
as possible and at the same time guarantee high recording quality. In general, microphones with
large membranes have better signal to noise ratio, and this allows better recording quality. Since
the membrane area here can not be reduced significantly any further, further miniaturization is
only possible if the area occupied by the frame to which the membrane is fixed can be reduced.
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[0003]
However, as this frame is made thinner, the problem of mechanical rigidity arises. Specifically, a
fixed backplate attached to the frame can exert force (s) on the frame, and if the frame is too thin,
the force bends the frame Bring. Furthermore, this frame transmits these forces to the abovementioned membrane, so that the measuring accuracy of this membrane is hampered by these
generated forces. In particular, for asymmetric membranes, for example oval, non-circular, and
rectangular, non-square membranes, the mechanical stresses generated thereby, for example
during large temperature changes, are This leads to a great deterioration of the measurement
accuracy of the membrane.
[0004]
The object of the present invention is therefore to make it possible to miniaturize the transducer
element without deteriorating the measuring properties of the membrane.
[0005]
This task is solved by the converter element according to claim 1 of the present application.
[0006]
The invention presents one transducer element, which comprises one movable membrane with
one edge, one frame in which the edge of the membrane is fixed, and one reinforcing member.
And the reinforcement member couples together one first portion (Teilabschnitt) of the frame
and one second portion of the frame opposite the first portion. .
[0007]
The above-mentioned reinforcing member may in particular be directly mechanically coupled
with the first portion of the above-mentioned frame and may be directly mechanically coupled
with the second portion of the above-mentioned frame.
The reinforcing member may in particular be configured to hold the first part of the frame and
the second part of the frame together at one fixed distance.
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Thus, the reinforcing member suppresses the forces acting on the frame that may cause the first
portion of the frame to move significantly relative to the second portion of the frame.
[0008]
The stiffening member may have a height corresponding to the height of the frame minus the
minimum distance between the stiffening member and the movable membrane.
Thereby, the reinforcement member can be provided such that the first and second parts of the
frame have the same distance from one another over the entire height of the reinforcement
member. Thereby, in particular, the first and second parts deform along their respective height
positions and, for example, at the lower end of the frame on the side not facing the membrane, It
can be prevented that the membrane has a greater distance than near the upper end of the frame
to which it is fixed.
[0009]
The stiffening members can thus be provided from the frame in such a way that less force is
exerted on the movable membrane. In particular, this reinforcing member can reduce the
components of the asymmetric forces exerted by the frame on the movable membrane.
[0010]
This is especially important in the case of asymmetric stress distributions, which can occur in
non-square or non-circular membranes. Specifically, in such a membrane, the above-described
reinforcing member as described above provides a very important improvement in recording
quality. Such an improvement would have been possible only if this frame was made much
thicker. However, even with symmetrical membranes, such as round or square, the abovementioned reinforcement members can provide an improvement, which enables a further
reduction of the wall thickness of the frame.
[0011]
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Overall, the above-mentioned reinforcement members make it possible to reduce the wall
thickness of the above-mentioned frame, and thus to further miniaturize this transducer element
without deteriorating the measuring accuracy of the present transducer element. Make it
possible.
[0012]
The above frame may, for example, be made of silicon.
The movable membrane and the fixed back plate are disposed at one upper end of the frame,
wherein the fixed back plate is fixed at a small distance to the membrane. There is. The edge of
the membrane may in particular be fixed to the frame so that the edge of the membrane can not
move in the direction of the plane normal of the membrane.
[0013]
The first and second parts described above are approximately from the lower end of the frame,
which is arranged on the side not facing the membrane, the minimum distance between the
reinforcement member and the membrane from the height of the frame It is stretched to a height
corresponding to the difference between These parts may, for example, be formed in a wedge or
band shape. The first and second portions are not directly adjacent to one another. Rather, other
parts exist between the first part and the second part.
[0014]
The expression "on the opposite side" here means that the first part described above and the
second part described above are not directly adjacent to one another. A connecting line
connecting any one point of the first part to any one point of the second part travels the inside of
the transducer element, wherein There is no crossing.
[0015]
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The transducer elements may be configured to convert acoustic signals or other pressure
fluctuations into electrical signals. Specifically, the transducer element is configured to convert
the audio signal into an electrical signal. This transducer element may be one MEMS element
(MEMS = micro-electro-mechanical system, Mikroelektromechanisches System).
[0016]
The above-mentioned reinforcing member may have a height smaller than the above-mentioned
height of the frame. Thus, the above-mentioned reinforcing member can be separated from the
above-mentioned movable membrane by one minimum distance. In this way it is ensured that the
membrane is placed on the reinforcing element so that the reinforcing element does not impede
the movement of the membrane. The minimum distance is, in particular, set such that, on
displacement of the membrane, the membrane does not immediately come into contact with the
reinforcing member.
[0017]
The above-mentioned reinforcing member and the above-mentioned frame may be made of the
same material. This material may in particular be silicon. Specifically, the above-mentioned
reinforcement member and the above-mentioned frame can be produced in one common
processing step, for example one etching process. From the above, the production of the abovementioned reinforcing member does not require any additional processing steps. The one etching
mask used to produce the frame described above is only correspondingly adjusted, so that this
etching mask together forms the reinforcing member described above. Thus, this reinforcing
member can be manufactured with minimal effort.
[0018]
Furthermore, the above-mentioned reinforcing member may couple together the third part of one
of the above-mentioned frames and the fourth part of one of the above-mentioned frames. The
fourth portion is on the opposite side of the third portion. The reinforcing member holds the
third and fourth portions at a fixed distance from one another. Specifically, the third and fourth
portions are held at one fixed distance from one another over the entire height of the reinforcing
member. Also for the first and second parts described above, the third and fourth parts are firmly
held in one firmly defined position by the above-mentioned reinforcing members.
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[0019]
The reinforcing member configured in this way can further reduce the above-mentioned
generated force (s) acting on the above-mentioned membrane. Depending on the shape of the
above selected membrane, the above frame may have more than one mechanical weakness. The
combination of the third and fourth parts described above could eliminate one second
mechanical weakness of the frame described above. In particular, none of the first to fourth part
of the above mentioned frame can be directly adjacent to the other one of this first to fourth part.
[0020]
The above reinforcing member may be in the form of a band. Specifically, the reinforcing
member is band-shaped in one plane parallel to the membrane in one cross section of the
transducer element. The reinforcing member may be in the form of a band over its entire height.
[0021]
In alternative embodiments, the above-mentioned reinforcing members may be cruciform or starshaped. These shapes are also in a plane parallel to the membrane, at the cross section of the
transducer element. Depending on the shape of the membrane and its associated frame, a bandshaped, cruciform or star-shaped reinforcing member may be advantageous. This reinforcement
must always be set in such a way that it evens out the mechanical weakness of the above
mentioned frame.
[0022]
The above membrane may be oval or rectangular. Specifically, this membrane may comprise one
asymmetric structure, for example one non-circular one oval or one non-square one rectangle. In
particular for membranes with such a degree of asymmetry, the use of the above-mentioned
reinforcing elements is particularly advantageous. This is because here the asymmetric forces act
on the frame described above, and these forces can have a major effect on the membrane without
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the above-mentioned reinforcement members, and the measurement of this membrane It may
deteriorate the accuracy. However, the above-mentioned reinforcing member can suppress this.
[0023]
The above reinforcing member may have a height in the range of 150 to 700 μm. Here, the
height of the reinforcing member should be adapted to the height of the above-mentioned frame.
This reinforcement must be made as high as possible in order to stabilize the frame over a large
range of its height, so that no immediate contact with the membrane takes place. There must be.
Correspondingly, there must be one minimum distance between the membrane and the
reinforcement without this reinforcement.
[0024]
According to another aspect, the invention relates to a single MEMS (MEMS = Micro-ElectroMechanical Systems) microphone, comprising a transducer element as described above.
[0025]
In the following, the present converter and preferred embodiments will be described in detail
with reference to the figures.
[0026]
1 shows a cross section of a transducer element with a reinforcing element according to a first
embodiment.
Fig. 2 shows a cross section of one of the transducer elements shown in Fig. 1;
Fig. 6 shows a simulation of the mechanical stress generated in an oval membrane of one
transducer element. This transducer element does not have any reinforcing members. Fig. 2
shows a cross section of one transducer element with one reinforcing element according to one
second embodiment. Fig. 6 shows a simulation of the mechanical stress generated in an oval
membrane of one transducer element. The transducer element comprises a reinforcing element
according to the first embodiment. Fig. 6 shows a simulation of the mechanical stress generated
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in an oval membrane of one transducer element. This transducer element comprises a reinforcing
member according to the second embodiment. Fig. 6 shows another example embodiment of a
transducer element with one reinforcing member according to the first embodiment. 6 shows
another exemplary embodiment of a transducer element with one reinforcing member according
to a second embodiment. Fig. 6 shows a portion of one transducer element.
[0027]
FIG. 1 shows one cross section of one transducer element 1. The transducer element 1 comprises
one movable membrane 2 and one fixed back plate 3. One voltage may be applied between the
membrane 2 and the back plate 3 so that the membrane 2 and the back plate 3 form one
capacitor. As a result of pressure fluctuations, when this membrane 2 moves relative to the
backplate 3, this changes the capacitance of this capacitor. In particular, sound waves can lead to
pressure fluctuations that change the capacitance of this capacitor. The transducer element 1 is
configured to convert pressure fluctuations into electrical signals. Specifically, the transducer
element 1 can convert one acoustic signal into one electrical signal.
[0028]
The transducer element 1 forms one front cavity and one back cavity. The front cavity is adapted
to be in pressure communication with the external environment of the transducer element 1.
Correspondingly, the transducer element 1 comprises one acoustic inlet opening (not shown),
through which the front cavity can be in pressure communication with the external environment,
and Sound waves or other pressure waves can reach the membrane 2 via this sound inlet
opening. The back cavity of this transducer element 1 is a reference cavity that is acoustically
separated from the above mentioned front cavity. This transducer element 1 is suitable for
measuring the time-varying difference between the sound pressure in the front cavity and the
sound pressure in the back cavity.
[0029]
Furthermore, the transducer element 1 comprises one vent opening for static pressure balance
between the front cavity and the back cavity. For this reason, there is no constant unchanging
pressure in the back cavity. Rather, the pressure in the back cavity slowly matches the external
environmental pressure via the vent opening.
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[0030]
The vent opening comprises one large acoustic impedance. Thus, sound waves can not penetrate
the back cavity through the vent opening.
[0031]
Furthermore, the movable membrane 2 comprises one edge 4, which is fixed to one frame 5 of
the transducer element 1. The edge 4 of the membrane 2 is fixed so that it can not move in the
direction towards or away from the backplate 3. Only the inner region 6 of the membrane 2
which is not fixed directly to the frame 5 is movable in the direction towards or away from the
backplate 3. The frame 5 of the transducer element 1 consists of silicon.
[0032]
FIG. 2 shows one cross section of the transducer element 1 along the line AA ′ shown in FIG.
[0033]
The shape of the frame 5 is adapted to the shape of the membrane 2.
This frame 5 can be divided into many parts. Specifically, this frame 5 comprises one first part 7
and one second part 8, wherein the first and second parts 7, 8 of this frame 5 are on the opposite
side to each other .
[0034]
Furthermore, the converter element 1 comprises one reinforcing member 10. The reinforcing
member 10 couples the first portion 7 of the frame 5 to the second portion 8 of the frame 5. The
reinforcing member 10 has a height somewhat smaller than the height of the frame 5. For
example, the height of the reinforcing member 10 may be 5 to 25 μm smaller than the height of
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the frame 5. From the above, the minimum distance 16 between the membrane 2 and the
reinforcing member 10 is such that the membrane 2 does not sit directly on the reinforcing
member 10. The reinforcing member 10 extends from one lower end 9 of the frame 5 on the
face of the frame 5 opposite the membrane 2 to an upper limit position 15 separated from the
membrane 2 by a minimum distance 16.
[0035]
According to one first exemplary embodiment, the reinforcing member 10 is in the form of a
band. The principle of operation of the reinforcing member 10 will be clear with reference to the
cross section shown in FIG.
[0036]
The reinforcing member 10 couples the first portion 7 of the frame 5 and the second portion 8
of the frame 5. The stiffening member 10 is such that less force is applied to the membrane 2
and in particular no asymmetrical force (s) acts on the membrane 2 or at least asymmetry to the
membrane 2. It acts so that the component of the acting force (s) is greatly reduced.
[0037]
The forces acting asymmetrically occur specifically as described below. The fixed back plate 3
has a large tension. The fixed back plate 3 thereby applies a force to the frame 5, which pulls the
frame 5 onto the upper end 17 of the frame in which the back plate is arranged. At the same
time, this force acts so that the frame 5 is pulled away at its lower end 9. The attraction of the
frame 5 to the upper end 17 also distorts the membrane 2 whose edge 4 is fixed to the upper
end 17 of the frame 5.
[0038]
In the first embodiment shown in FIG. 2, the membrane 2 has an elliptical shape. The oval shape
defines one main axis 11 and one auxiliary axis 12, which are perpendicular to the main axis 11
and shorter than this main axis 11.
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[0039]
FIG. 3 shows a simulation of the mechanical stress acting on the oval membrane 2a without the
reinforcing member 10. This oval membrane 2a is very similar to the oval membrane 2 shown in
FIG. The left figure shows the mechanical stress acting in the x direction and the right figure
shows the mechanical stress acting in the y direction. Here, the x-direction is defined by the two
most distant points of the membrane 2a, and the y-direction is a direction perpendicular to the xdirection. The major axis 11 of the elliptical membrane 2 extends in the x direction, and the
minor axis 12 extends in the y direction.
[0040]
It can be clearly seen in FIG. 3 that one significant mechanical stress is generated along the x
direction of the membrane 2a. The average mechanical stress along the x direction is 49.6 MPa.
The average mechanical stress along this y direction is 38.7 MPa. As a whole, the difference in
average mechanical stress in the x direction and in the y direction in the oval membrane 2a
without the reinforcing member 10 is 10.9 MPa.
[0041]
The reason for the uneven mechanical stress distribution in the x and y directions is that the
frame 5 is weaker in the x direction than in the y direction because of the large elongation of its
membrane 2. This causes the membrane 2 to be distorted more in the x-direction than in the ydirection due to the force applied from the fixed backplate 3 to the frame 5.
[0042]
The reinforcing member 10 is used such that the first and second parts 7, 8 of the frame 5 are
held at a fixed distance from one another. The frame 5 is thus held firmly in such a way that the
parts 7, 8 are at a fixed distance from one another, from its lower end 9 to a height
corresponding to the minimum distance between the membrane 2 and the reinforcing member
10. This fixed distance is predetermined by the length of the reinforcing member 10. From the
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above, it is possible to suppress that the frame 5 can move largely at its upper end. This causes
less force (s) to be applied to the membranes 2, 2a. The provision of the reinforcing element 10
described here in the mechanically weakened part of the frame 5 makes it possible in particular
to reduce asymmetric components of the forces acting on the membrane 2, 2a.
[0043]
FIG. 4 shows an example of a second embodiment of the reinforcing member 10a. Here, the
reinforcing member 10a is formed in a cross shape. Here, in addition to the first and second
parts 7 and 8 of the frame 5, the reinforcing member 10 a likewise has one third part 13 of the
frame 5 opposite to this third part 13. , And a fourth portion 14 of this frame 5. The third and
fourth portions 13, 14 are also held at a fixed distance from one another. Furthermore, again, the
third and fourth portions 13, 14 are held by the reinforcing member 10a in one defined position
relative to the first and second portions 7, 8. The third and fourth portions 13 and 14 of the
frame 5 also extend from the lower end 9 of the frame 5 to the upper limit position 15 thereof,
thus leaving a minimum distance 16 between the reinforcing member 10a and the membrane 2
It is in the state of
[0044]
FIGS. 5 and 6 show the generated mechanical forces, respectively, which act on the oval
membrane 2a. Here, in FIG. 5, a band-shaped reinforcing member 10 according to the first
embodiment is provided, and in FIG. 6, a cross-shaped reinforcing member 10a according to the
second embodiment is provided. In FIGS. 5 and 6, the left-hand figures show the mechanical
stress acting in the x-direction and the right-hand figures show the mechanical stress acting in
the y-direction.
[0045]
It can be seen that the occurrence of mechanical stresses acting on the membrane 2a is
significantly reduced compared to the exemplary embodiment without the reinforcement
member 10. In the embodiment having the band-shaped reinforcing member 10 shown in FIG. 5,
the average mechanical stress along the x-direction is 47.4 MPa. The average mechanical stress
along the y direction is 42.4 MPa. As a whole, the difference in mean mechanical stress in the x
direction and the y direction in the oval membrane 2a having the band-shaped reinforcing
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member 10 is 5.0 MPa.
[0046]
In the embodiment having the band-shaped reinforcing member 10a shown in FIG. 6, the average
mechanical stress along the x direction is 47.3 MPa. The average mechanical stress along the y
direction is 42.2 MPa. As a whole, the difference between the average mechanical stress in the x
direction and the y direction in the oval membrane 2a having the cross-shaped reinforcing
member 10a is 5.1 MPa.
[0047]
That is, both the belt-shaped reinforcing member 10 and the cross-shaped reinforcing member
10a significantly reduce the difference of 10.9 Pa in the average mechanical stress in the x
direction and the y direction to 5.0 MPa or 5.1 MPa. Is bringing. As described above, the bandshaped reinforcing member 10 or the cross-shaped reinforcing member 10a is used so that the
mechanical stress is evenly distributed in the membrane 2a.
[0048]
Here, substantially no improvement is seen between the reinforcing member 10 of the first
embodiment and the reinforcing member 10a of the second embodiment. This is due to the
special shape of the frame 5 that is significantly less rigid in one direction than in another. Along
the x-axis, this frame 5 comprises a substantially straight part, which deforms relatively easily.
Along the y-axis, this frame 5 is semi-circular in shape, which makes it relatively difficult to
deform. On the other hand, in the frame 5 or the membrane 2 formed in another form, the crossshaped configuration of the reinforcing member 10a significantly enhances this mechanical
rigidity as compared with the band-shaped configuration. it can.
[0049]
7 and 8 show another exemplary embodiment of the transducer element 1. In FIG. 7 and FIG. 8,
these membranes 2b are each formed in a rectangular shape. In FIG. 7, the reinforcing member
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10 has a band shape, and in FIG. 8, the reinforcing member 10 a has a cross shape.
[0050]
Furthermore, other shapes of the reinforcement member are also possible, for example the
reinforcement member may be star-shaped. The shape of these selected reinforcement members
will always be adapted to the shape of the membrane.
[0051]
FIG. 9 shows a part of the transducer element 1 and with reference to this figure, a method of
manufacturing this transducer element 1 will be schematically described.
[0052]
The frame 5 and the reinforcing member 10 are manufactured in one common etching step, in
which one mask is attached on one silicon wafer and then a part of the silicon wafer is etched
away, The front cavity of this transducer element 1 is thus formed.
The frame 5 and the reinforcement member 10 are thus manufactured by photolithography from
this silicon wafer.
[0053]
Thus, this reinforcing member 10 is manufactured in this etching step to create one cavity in one
silicon block. This method is called deep reactive ion etching (DRIE). This method can result in a
negative tilt angle α at the sidewall of the cavity, depending on the choice of process
parameters, which is also found on the sidewall of the stiffening member 10. The height H of the
reinforcing member 10 is adjusted by the etching angle α and the width W of the mask used
therefor.
[0054]
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Various forms of the reinforcing member 10 are shown in FIG. In the widths W1, W2 and W3,
the reinforcing member 10 has a height H, respectively. The height of the reinforcing member 10
having the width W4 or W5 is H4 or H5.
[0055]
Depending on the mask used, and depending on the etching angle α described above, this
reinforcing member 10 may be scalloped with a stump top or pointed towards the membrane 2.
This process is adjusted so that the reinforcing member 10 is separated by a minimum distance
from the membrane 2. Furthermore, the etching process can be modified such that the etching
angle α can be varied to produce reinforcing members 10 of different widths having the same
height.
[0056]
1: Transducer elements 2, 2a, 2b: Membrane 3: Backplate 4: Edge of membrane 5: Frame 6: Inner
area of membrane 7: First part 8: Second part 9: Bottom end of frame 10, 10a: Reinforcement
member 11: Main shaft 12: Secondary shaft 13: Third portion 14: Fourth portion 15: Upper limit
position 16: Minimum distance 17: Upper end of frame
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