MEMS device having a tiltable suspended structure controlled by electromagnetic actuation

Patent metadata

Field	Value
Publication number	US-11681141-B2
Application number	US-201916705677-A
Country	US
Kind code	B2
Filing date	Dec 6, 2019
Priority date	Dec 14, 2018
Publication date	Jun 20, 2023
Grant date	Jun 20, 2023

Abstract

A MEMS device is obtained by forming a temporary biasing structure on a semiconductor body, and forming an actuation coil on the semiconductor body, the actuation coil having at least one first end turn, one second end turn and an intermediate turn arranged between the first and the second end turns and electrically coupled to the first end turn through the temporary biasing structure. In this way, the intermediate turn is biased at approximately the same potential as the first end turn during galvanic growth, and, at the end of growth, the actuation coil has an approximately uniform thickness. At the end of galvanic growth, portions of the temporary biasing structure are selectively removed to electrically separate the first end turn from the intermediate turn and from a dummy biasing region adjacent to the first end turn.

First claim

The invention claimed is:

1. A method for manufacturing a MEMS device, the method comprising:
forming a temporary biasing structure on a semiconductor body;
forming an actuation coil on the semiconductor body, the actuation coil having a first end turn, a second end turn, and an intermediate turn, the intermediate turn being arranged between the first end turn and the second end turn and electrically coupled to the first end turn through the temporary biasing structure;
selectively removing portions of the temporary biasing structure to thereby electrically separate the first end turn from the intermediate turn and from a dummy biasing region adjacent to the first end turn; and
selectively removing portions of the semiconductor body to define a fixed structure, a suspended structure carrying the actuation coil and carried by the fixed structure, and a supporting structure coupling the suspended structure to the fixed structure and configured to allow at least one degree of freedom to the suspended structure with respect to the fixed structure.

2. The method according to claim 1 , wherein forming the temporary biasing structure comprises:
forming a passivation layer on the semiconductor body;
forming a buried conductive region within the passivation layer and having first and second contact portions;
forming a seed structure of conductive material on the passivation layer, the seed structure comprising a first seed portion in electrical contact with the first contact portion, a second seed portion in electric contact with the second contact portion and belonging to the dummy biasing region, and a third seed portion, the second seed portion and the third seed portion being contiguous with each other and in mutual electric contact with each other;
selectively covering the seed structure; and
galvanically growing the actuation coil on the seed structure by growing the intermediate turn on the first seed portion and at least part of the first end turn on the third seed portion, wherein the buried conductive region maintains the first seed portion at a same potential as the third seed portion through the second seed portion.

3. The method according to claim 2 , wherein the first end turn is an inner turn of the actuation coil, wherein the second end turn is an outer turn of the actuation coil, and wherein the dummy biasing region is adjacent to the inner turn.

4. The method according to claim 2 , wherein the forming the buried conductive region comprises:
forming a conductive layer and patterning the conductive layer to shape the buried conductive region and at least one electrical connection region having a first connection portion in electric contact with the first end turn and a second connection portion; and
forming an electrically conductive region on the fixed structure and in electric contact with the second connection portion of the electric connection region.

5. The method according to claim 2 , wherein forming the seed structure comprises forming a seed layer and patterning the seed layer to form the second seed portion and a coil-shaped seed region including the first and the third seed portions, and wherein selectively removing portions of the temporary biasing structure comprises removing parts of the seed layer between the first end turn and the dummy biasing region.

6. The method according to claim 2 , wherein forming a seed structure comprises forming a seed layer; wherein selectively covering the seed structure comprises forming a galvanic growth mask having a coil-shaped opening; wherein, after galvanically growing the actuation coil, the galvanic growth mask is removed; and wherein selectively removing portions of the seed layer comprises removing parts of the seed layer between the turns of the actuation coil and portions between the first end turn and the dummy biasing region.

7. The method according to claim 2 , wherein the seed structure has a first thickness and the buried conductive region has a second thickness, greater than the first thickness.

8. The method according to claim 7 , wherein the seed structure has a thickness comprised between 50 and 500 nm and the buried conductive region has a thickness comprised between 300 and 700 nm.

9. The method according to claim 2 , wherein the seed structure is comprised of a metal chosen among copper, copper alloy and gold, and wherein the buried conductive region is comprised of a metal chosen among gold, aluminum and copper.

10. A MEMS device, comprising:
a fixed structure;
a suspended structure carried by the fixed structure;
a supporting structure, coupling the suspended structure to the fixed structure and configured to allow at least one degree of freedom to the suspended structure with respect to the fixed structure;
an actuation coil extending on the suspended structure, the actuation coil comprising a first end turn, a second end turn, and an intermediate turn arranged between the first end turn and the second end turn; and
a dummy biasing structure comprising a dummy biasing region adjacent to the first end turn and electrically coupled to the intermediate turn.

11. The MEMS device according to claim 10 , wherein the first end turn is an inner turn of the actuation coil, wherein the second end turn is an outer turn of the actuation coil, and wherein the dummy biasing region is adjacent to the inner turn.

12. The MEMS device according to claim 10 , wherein the dummy biasing structure comprises a buried conductive region extending underneath the actuation coil.

13. The MEMS device according to claim 12 , further comprising a passivation layer extending between the suspended structure and the actuation coil, wherein the buried conductive region extends in the passivation layer and is electrically coupled to the intermediate turn and to the dummy biasing region through electrical connection portions extending through the passivation layer.

14. The MEMS device according to claim 13 , further comprising an electrically conductive region formed in the fixed structure and an electrical connection region extending inside the passivation layer between the electrically conductive region and the first end turn, the electrical connection region being formed in a same conductive material layer of the buried conductive region.

15. The MEMS device according to claim 12 , wherein the first end turn, second end turn, and intermediate turn of the actuation coil each comprise a seed region and a conductive mass arranged on the seed region; and wherein the dummy biasing structure comprises a dummy seed portion formed in a same seed layer of the seed region of the first end turn, second end turn, and intermediate turn.

16. The MEMS device according to claim 10 , forming a MEMS micromirror.

17. A MEMS device, comprising:
a fixed structure;
a suspended structure carried by the fixed structure;
a supporting structure coupling the suspended structure to the fixed structure;
an actuation coil extending on the suspended structure, the actuation coil comprising a first end turn, a second end turn, and an intermediate turn arranged between the first end turn and the second end turn; and
a dummy biasing structure comprising a dummy biasing region electrically coupled to the intermediate turn.

18. The MEMS device according to claim 17 , wherein the first end turn is an inner turn of the actuation coil, and wherein the second end turn is an outer turn of the actuation coil.

19. The MEMS device according to claim 17 , wherein the dummy biasing structure comprises a buried conductiv

Assignees

• St Microelectronics Srl

Inventors

• Carminati Roberto
• Costantini Sonia
• Gianola Riccardo
• Montagna Linda
• Carpignano Francesca Maria Carla

Classifications

• B81B2203/04

  Electrodes · CPC title

• B81B2201/042

  Micromirrors, not used as optical switches · CPC title

• B81B2203/0154

  Torsion bars · CPC title

• B81C2201/016

  Passivation · CPC title

• B81B3/0045

  Improve properties related to angular swinging, e.g. control resonance frequency · CPC title