Electromechanical transducer device and method of forming a electromechanical transducer device
View Patent ↗A micro or nano electromechanical transducer device formed on a semiconductor substrate comprises a movable structure which is arranged to be movable in response to actuation of an actuating structure. The movable structure comprises a mechanical structure comprising at least one mechanical layer having a first thermal response characteristic and a first mechanical stress response characteristic, at least one layer of the actuating structure, the at least one layer having a second thermal response characteristic different to the first thermal response characteristic and a second mechanical stress response characteristic different to the first mechanical stress response characteristic, a first compensation layer having a third thermal response characteristic and a third mechanical stress characteristic, and a second compensation layer having a fourth thermal response characteristic and a fourth mechanical stress response characteristic. The first and second compensation layers are arranged to compensate a thermal effect produced by the different first and second thermal response characteristics of the mechanical structure and the at least one layer of the actuating structure such that movement of the movable structure is substantially independent of variations in temperature and to adjust a stress effect produced by the different first and second stress response characteristics of the mechanical structure and the at least one layer of the actuating structure such that the movable structure is deflected a predetermined amount relative to the substrate when the electromechanical transducer device is in an inactive state.
1. A micro or nano electromechanical transducer device formed on a semiconductor substrate comprising:
a movable structure being arranged to be movable in response to actuation of an actuating structure and comprising:
a mechanical structure having at least one mechanical layer having a first thermal response characteristic and a first mechanical stress response characteristic;
at least one layer of the actuating structure, the at least one layer having a second thermal response characteristic different to the first thermal response characteristic and a second mechanical stress response characteristic different to the first mechanical stress response characteristic;
a first compensation layer having a third thermal response characteristic and a third mechanical stress characteristic; and
a second compensation layer having a fourth thermal response characteristic and a fourth mechanical stress response characteristic,
wherein the first and second compensation layers are arranged to compensate a thermal effect produced by the different first and second thermal response characteristics of the mechanical structure and the at least one layer of the actuating structure such that movement of the movable structure is substantially independent of variations in temperature and to adjust a stress effect produced by the different first and second stress response characteristics of the mechanical structure and the at least one layer of the actuating structure such that the movable structure is deflected a predetermined amount relative to the substrate when the electromechanical transducer device is in an inactive state.
2. The micro or nano electromechanical transducer device of claim 1 , wherein the movable structure is formed over a surface of the semiconductor substrate and the predetermined amount includes a predetermined range of deflection values relative to a plane parallel to the surface of the semiconductor substrate.
3. The micro or nano electromechanical transducer device of claim 1 , wherein the predetermined amount includes zero deflection.
4. The micro or nano electromechanical transducer device of claim 1 , wherein the first compensation layer is a thermal compensation layer and the second compensation layer is a stress compensation layer, wherein the thermal compensation layer is arranged to compensate the thermal effect and the stress compensation layer is arranged to compensate the stress effect.
5. The micro or nano electromechanical transducer device of claim 4 , wherein the stress compensation layer is arranged to have a fourth thermal response characteristic which is substantially the same as the first thermal response characteristic.
6. The micro or nano electromechanical transducer device of claim 4 , wherein the stress compensation layer is adjacent the mechanical structure.
7. The micro or nano electromechanical transducer device of claim 4 , wherein the mechanical structure and the stress compensation layer are formed from the same type of material with different levels of stress.
8. The micro or nano electromechanical transducer device of claim 4 , wherein the thermal compensation layer is different to the at least one layer of the actuating structure.
9. The micro or nano electromechanical transducer device of claim 4 , wherein the thermal compensation layer is adjacent the mechanical structure on a side of the mechanical structure opposite to the stress compensation layer.
10. The micro or nano electromechanical transducer device of claim 4 , wherein the at least one layer of the actuating structure is formed of a first material and the thermal compensation layer is formed of a second material different to the first material.
11. The micro or nano electromechanical transducer device of claim 4 , wherein the thermal compensation layer and the at least one layer of the actuating structure forming part of the movable structure are formed on opposite sides of the mechanical structure.
12. The micro or nano electromechanical transducer device of claim 1 , wherein the actuating structure includes a plurality of layers and the plurality of layers form part of the movable structure, the movable structure being movable in response to actuation of the plurality of layers.
13. The micro or nano electromechanical transducer device of claim 12 , wherein the plurality of layers includes a piezoelectric layer formed between first and second electrode layers.
14. The micro or nano electromechanical transducer device of claim 12 , wherein the actuating structure further comprises a layer formed on the semiconductor substrate.
15. The micro or nano electromechanical transducer device of claim 1 , wherein the at least one layer of the actuating structure forming part of the movable structure occupies a first area in a plane substantially parallel to the mechanical structure and wherein the first and second compensation layers occupy a second area in a plane substantially parallel to the mechanical structure, wherein the second area is substantially the same as the first area.
16. The micro or nano electromechanical transducer device of claim 1 , wherein the first and second compensation layers are formed from materials selected according to the Coefficient of Thermal Expansion and Young's modulus of the materials, and wherein each of the first and second compensation layers has a predetermined thickness in order to compensate the thermal and stress effects.
17. The micro or nano electromechanical transducer device of claim 16 , wherein the first compensation layer is a thermal compensation layer and the second compensation layer is a stress compensation layer, wherein the predetermined thickness of the thermal compensation layer is obtained by solving the following equation:
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and wherein the predetermined thickness of the stress compensation layer is obtained by solving the following equation:
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Where:
Ei is the Young's modulus of layer i;
ti is the thickness of layer i;
αi is the CTE of layer i;
dij is the distance between layers i and j, measured from the middle of the layers;
σi is the residual stress in layer i; and
zij is equal to 1 when layer j is above layer i and equals to −1 when layer j is below layer i.
18. A method of forming a micro or nano electromechanical transducer device on a semiconductor substrate, the micro or nano electromechanical transducer device comprising a movable structure being arranged to be movable in response to actuation of an actuating structure, the method comprising forming the movable structure by:
providing a mechanical structure comprising at least one mechanical layer having a first thermal response characteristic and a first mechanical stress response characteristic;
providing at least one layer of the actuating structure, the at least one layer having a second thermal response characteristic different to the first thermal response characteristic and a second mechanical stress response characteristic different to the first mechanical stress response characteristic;
providing a first compensation layer having a third thermal response characteristic and a third mechanical stress characteristic,
providing a second compensation layer having a fourth thermal response characteristic and a fourth mechanical stress response characteristic,
wherein the first and second compensation layers are arranged to compensate a thermal effect produced by the different first and second thermal response characteristics of the mechanical structure and the at least one layer of the actuating structure such that movement of the movable structure is substantially independent of variations in temperature and to adjust a stress effect produced by the different first and second stress response characteristics of the mechanical structure and the at least one layer of the actuating structure such that the movable structure is deflected a predetermined amount relative to the substrate when the electromechanical transducer device is in an inactive state.
19. The method of claim 18 , wherein the movable structure is formed over a surface of the semiconductor substrate and the predetermined amount includes a predetermined range of deflection values relative to a plane parallel to the surface of the semiconductor substrate.
20. The method of claim 18 , wherein the predetermined amount includes zero deflection.
21. The method of claim 18 , wherein the first compensation layer is a thermal compensation layer and the second compensation layer is a stress compensation layer, wherein the thermal compensation layer is arranged to compensate the thermal effect and the stress compensation layer is arranged to compensate the stress effect.
22. The method of claim 21 , further comprising selecting materials for the thermal compensation layer and the stress compensation layer according to the Coefficient of Thermal Expansion and Young's modulus of the materials, and arranging for each of the temperature and stress compensation layers to have predetermined thicknesses in order to compensate the thermal and stress effects.
23. The method of claim 22 , wherein the predetermined thickness of the thermal compensation layer is obtained by solving the following equation:
∑
i
∑
j
>
i
d
ij
·
E
i
·
E
j
·
t
i
·
t
j
(
α
i
-
α
j
)
·
z
ij
·
Δ
T
0
=
0
,
and wherein the predetermined thickness of the stress compensation layer is obtained by solving the following equation:
∑
i
∑
j
>
i
d
ij
·
E
i
·
E
j
·
t
i
·
t
j
(
σ
j
E
j
-
σ
i
E
i
)
·
z
ij
=
0
Where:
Ei is the Young's modulus of layer i;
ti is the thickness of layer i;
αi is the CTE of layer i;
dij is the distance between layers i and j, measured from the middle of the layers;
σi is the residual stress in layer i; and
zij is equal to 1 when layer j is above layer i and equals to −1 when layer j is below layer i.