MEMS ultrasonic transducer device with improved damping of the oscillations of a membrane of the same, and manufacturing process of the same
MEMS ultrasonic transducer, MUT, device, comprising a semiconductor body with a first and a second main surface and including: a first chamber extending into the semiconductor body at a distance from the first main surface; a membrane formed by the semiconductor body between the first main surface and the first chamber; a piezoelectric element on the membrane; a second chamber extending into the semiconductor body between the first chamber and the second main surface; a central fluidic passage extending into the semiconductor body from the second main surface to the first chamber and traversing the second chamber; and one or more lateral fluidic passages extending into the semiconductor body from the second main surface to the second chamber. The one or more lateral fluidic passages, the central fluidic passage and the second chamber define a fluidic recirculation path that fluidically connects the first chamber with the outside of the semiconductor body.
1 . A device, comprising:
a semiconductor body of semiconductor material having a first and a second main surface and integrating a first MUT element which includes:
a first chamber extending into the semiconductor body at a distance from the first main surface;
a membrane formed by the semiconductor body between the first main surface and the first chamber;
a piezoelectric element extending on the first main surface of the semiconductor body above the membrane;
a second chamber extending into the semiconductor body between the first chamber and the second main surface;
a central fluidic passage extending into the semiconductor body from the second main surface to the first chamber and traversing the second chamber; and
one or more lateral fluidic passages extending into the semiconductor body from the second main surface to the second chamber,
wherein the one or more lateral fluidic passages, the central fluidic passage and the second chamber define a fluidic recirculation path that fluidically connects the first chamber with the outside of the semiconductor body.
2 . The device according to claim 1 , configured to be immersed in a liquid or gaseous propagation medium that extends from the outside of the semiconductor body to the first chamber,
wherein the fluidic recirculation path is configured to allow the recirculation of the propagation medium between the first chamber and the outside of the semiconductor body, the recirculation being caused by the alternate succession of expansions and contractions of a volume of the first and the second chambers, which are generated by oscillations of the membrane and which pump the propagation medium into and, respectively, out of the first chamber.
3 . The device according to claim 1 , wherein the first and second chambers are concentric and aligned along a central axis of the first MUT element, orthogonal to the first main surface,
wherein the central fluidic passage is arranged centrally with respect to the first and second chambers and is aligned along the central axis, and
wherein the one or more lateral fluidic passages are radially external with respect to the central fluidic passage around the central axis.
4 . The device according to claim 3 , wherein the one or more fluidic lateral passages are a plurality of the lateral fluidic passages which are arranged around the central fluidic passage.
5 . The device according to claim 4 , wherein the plurality of lateral fluidic passages have, parallel to the second main surface, a curved shape and laterally surround, at a distance, the central fluidic passage.
6 . The device according to claim 1 , wherein the first and second chambers have a circular shape or have a polygonal shape.
7 . The device according to claim 1 , further comprises a plurality of electrical connection lines and a control unit, the plurality of electrical connection lines configured to selectively couple at least one of the first and second electrodes of the first MUT element to the control unit, and wherein the piezoelectric element comprises a layer stack including a first and a second electrode and a thin-film piezoelectric region arranged between the first and second electrodes.
8 . The device according to claim 1 , wherein the central fluidic passage is formed by a central trench which defines a central opening in the second main surface, and
wherein the one or more lateral fluidic passages are formed by one or more respective lateral trenches, each defining a respective lateral opening in the second main surface.
9 . The device according to claim 1 , further comprising one or more second MUT elements, each of the one or more second MUT elements including:
a respective first chamber extending into the semiconductor body at a distance from the first main surface;
a respective membrane formed by the semiconductor body between the first main surface and the first chamber of the second MUT element;
a respective piezoelectric element extending on the first main surface of the semiconductor body above the membrane of the second MUT element;
a respective second chamber extending into the semiconductor body between the first chamber of the second MUT element and the second main surface;
a respective central fluidic passage extending into the semiconductor body from the second main surface to the first chamber of the second MUT element and traversing the second chamber of the second MUT element; and
one or more respective lateral fluidic passages extending into the semiconductor body from the second main surface to the second chamber of the second MUT element,
wherein the one or more lateral fluidic passages, the central fluidic passage and the second chamber of the second MUT element define a respective fluidic recirculation path that fluidically connects the first chamber of the second MUT element with the outside of the semiconductor body.
10 . A device, comprising:
a semiconductor body of semiconductor material having a first main face and a second main face opposite to the first main face;
a first chamber within the semiconductor body;
a second chamber within the semiconductor body, the second chamber is between the first chamber and the second main face;
a central fluidic passage that extends into the second main face, extends through the second chamber, and extends to the first chamber;
a plurality of lateral fluidic passages extends into the second main face to the second chamber, and each respective lateral fluidic passage of the plurality of lateral fluidic passages is spaced laterally outward from the central fluidic passage;
a membrane that extends from the first chamber to the first main face; and
a piezoelectric element on the first main face of the semiconductor body, and the piezoelectric element fully overlaps the central fluid passage.
11 . The device of claim 10 , wherein the first chamber is spaced apart from the second chamber by a distance that is within a range from 3 micrometers (μm) to 40 micrometers (μm), or is equal to a lower end or an upper end of the range.
12 . The device of claim 10 , wherein the respective lateral fluidic passages of the plurality of lateral fluidic passages are curved.
13 . The device of claim 10 , wherein the membrane is concentric with the first chamber and the second chamber.
14 . The device of claim 10 , wherein a first center of the central fluidic passage, a second center of the first chamber, a third center of the second chamber, a fourth center of the membrane, and a fifth center of the piezoelectric element are along a central axis, and the central axis is transverse to the first main surface and a second main surface of the semiconductor body.
15 . A device, comprising:
a semiconductor body of semiconductor material having a first main face and a second main face opposite to the first main face;
a first chamber within the semiconductor body, the first chamber having a first diameter;
a second chamber within the semiconductor body, the second chamber is between the first chamber and the second main face, the second chamber having a second diameter less than the first diameter;
a central fluidic passage that extends into the second main face, extends through the second chamber, and extends to the first chamber, the central fluidic passage includes a third diameter less than the first diameter and less than the second diameter;
a plurality of lateral fluidic passages extends into the second main face to the second chamber, and each respective lateral fluidic passage of the plurality of lateral fluidic passages is spaced laterally outward from the central fluidic passage;
a membrane that extends from the first chamber to the first main face, the membrane being concentric with the first chamber and the second chamber; and
a piezoelectric element on the first main face of the semiconductor body, and the piezoelectric element fully overlaps the central fluid passage.
16 . The device of claim 15 , wherein the piezoelectric element is concentric with the central fluidic passage, the first chamber, the second chamber, and the membrane.
17 . The device of claim 15 , wherein the piezoelectric element has a fourth diameter that is less than the first diameter, less than the second diameter, and greater than the third diameter.
18 . The device of claim 15 , wherein the respective fluidic passages of the plurality of lateral fluidic passages are curved.
19 . The device of claim 15 , wherein the first chamber is spaced apart from the second chamber by a distance that is within a range from 3 micrometers (μm) to 40 micrometers (μm), or is equal to a lower end or an upper end of the range.
20 . The device of claim 15 , wherein a first center of the central fluidic passage, a second center of the first chamber, a third center of the second chamber, a fourth center of the membrane, and a fifth center of the piezoelectric element are along a central axis, and the central axis is transverse to the first main surface and the second main face of the semiconductor body.