MEMBRANE OF AMORPHOUS CARBON AND MEMS INCLUDING SUCH A MEMBRANE

Abstract

A microelectromechanical system includes a membrane of amorphous carbon having a thickness between 1 nm and 50 nm, and for example between 3 nm and 20 nm.

Claims

1. A membrane of amorphous carbon for a microelectromechanical system, the membrane of amorphous carbon having a thickness between 1 mm and 50 nm, wherein the membrane of amorphous carbon has an sp.sup.3 type hybridization rate between 20% and 40%.

2. The membrane according to claim 1, wherein the thickness is between 3 nm and 20 nm.

3. A microelectromechanical system including a membrane of amorphous carbon according to claim 1.

4. A microelectromechanical system including a movable membrane including a membrane of amorphous carbon according to claim 1.

5. The microelectromechanical system according to the claim 4, wherein the movable membrane includes a main membrane, the main membrane being coated with the membrane of amorphous carbon.

6. The microelectromechanical system according to claim 3, wherein the microelectromechanical system is an actuator.

7. The microelectromechanical system according to claim 3, wherein the microelectromechanical system is a sensor.

8. The microelectromechanical system according to claim 3, wherein the microelectromechanical system is a capacitive transducer.

9. The microelectromechanical system according to claim 3, wherein the microelectromechanical system is a piezoelectric transducer.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0022] Further characteristics and benefits of the invention will appear upon reading the following detailed description, with reference to the accompanying figures, which show:

[0023] FIG. 1, a schematic representation of a microelectromechanical system according to an embodiment of the invention;

[0024] FIG. 2, a schematic representation of a microelectromechanical system according to another embodiment of the invention;

[0025] FIG. 3, a schematic representation of a microelectromechanical system according to another embodiment of the invention; and

[0026] FIG. 4, a schematic representation of a microelectromechanical system according to another embodiment of the invention.

DETAILED DESCRIPTION

[0027] FIG. 1 represents a microelectromechanical system 1 according to an embodiment of the invention. The microelectromechanical system 1 is a capacitive transducer. It includes a stationary armature 2 and a movable membrane 3, separated by a cavity 4. Displacement of the movable membrane 2 can be caused either by a pressure of the external medium 7 if the transducer operates in a sensor mode, or by an electric voltage if the transducer operates in an actuator mode.

[0028] The movable membrane 3 includes a membrane 5 of amorphous carbon. This membrane 5 of amorphous carbon has a thickness between 2 nm and 50 nm.

[0029] FIG. 2 represents a microelectromechanical system according to another embodiment of the invention. This microelectromechanical system 1 is a capacitive transducer. It includes a stationary armature 2 and a movable membrane 3, separated by a cavity 4. The displacement of the movable membrane 3 can be caused either by a pressure of the external medium 7 if the transducer operates in a sensor mode, or by an electric voltage if the transducer operates in an actuator mode.

[0030] The movable membrane 3 includes a main membrane 6 coated with a membrane 5 of amorphous carbon. The membrane 5 of amorphous carbon has a thickness between 1 nm and 50 nm, and for example between 3 nm and 20 nm in an embodiment, so as not to modify the rigidity of the main membrane 6. The membrane 5 of amorphous carbon can be deposited either by direct deposition onto the main membrane, or by layer transfer.

[0031] FIG. 3 represents another embodiment in which the microelectromechanical system 1 is a piezoelectric transducer. In this embodiment, the microelectromechanical system includes a movable membrane 3 on which at least one piezoelectric sensor 8 or piezoelectric actuator 8 is attached. The movable membrane 3 includes, as in the previous embodiment, a main membrane 6 coated with a membrane 5 of amorphous carbon. The membrane 5 of amorphous carbon has a thickness between 1 nm and 50 nm, and for example between 3 nm and 20 nm in an embodiment, so as not to modify rigidity of the main membrane 6. The membrane of amorphous carbon can be deposited either by direct deposition onto the main membrane, or by layer transfer.

[0032] With reference to FIG. 4, it could also be considered that the movable membrane includes only the membrane of amorphous carbon as in the embodiment of FIG. 1. In this case, the piezoelectric sensors or actuators are attached beneath the membrane. In other words, in this case, the membrane includes a first face intended to be in contact with the external medium 7 and a second face on which the piezoelectric sensor(s) or actuator(s) 8 are attached. The benefit of this configuration is that the rigidity of the membrane is minimum, and therefore, transduction between mechanical movement of the membrane and electric signal across the piezoelectric sensors or actuators, for control or reading, is made in a minimum energy. The membrane of amorphous carbon has a thickness between 2 nm and 50 nm, determined as a function of the positioning of the piezoelectric sensors or actuators 8.

[0033] The membrane of amorphous carbon used in the microelectromechanical systems of FIGS. 1 to 4 has an sp.sup.3 type hybridization rate between 20% and 40% which enables it to have a Young's modulus between 100 GPa and 500 GPa. Indeed, the carbon atoms hybridize their outer orbitals s and p into sp.sup.2 and sp.sup.3 to form π or σ type bonds, the relative rates of these bonds is decisive for the properties of the material: basically, u bonds govern the electronic behavior of the membrane, and a bonds determine the mechanical behavior thereof. The rate of appearance of each of both bonds in the material can be experimentally determined by X-ray photoelectron spectrometry or by Raman spectroscopy. The sample is degassed during the measurement.

[0034] The membrane of amorphous carbon 5 is flexible. Indeed, the membrane of amorphous carbon has a Young's modulus between 100 GPa and 500 GPa.

[0035] The membrane 5 of amorphous carbon is chemically inert, biocompatible, hermetic even with nanosize thicknesses, and stable up to temperatures higher than 300° C. The membrane 5 of amorphous carbon enables both the main membrane 6 to be protected from aggressions of the external medium 7 and also the external medium to be protected from contaminations generated by the main membrane 6, the support 2, and all the elements of the MEMS, which is particularly interesting when the external medium is a biological medium.

[0036] Such a membrane of amorphous carbon can be for example manufactured in the device described in application FR no. 1560224. Indeed, this device allows manufacture of low thickness continuous homogenous elastic layers of amorphous carbon, the sp.sup.3 bond rate of which is higher than 20%, and on any type of substrate.

[0037] It will be appreciated that the invention is not limited to be embodiments described with reference to the figures and alternatives could be considered without departing from the scope of the invention. The membrane of amorphous carbon could be for example used in other microelectromechanical systems than those described with reference to the figures.