MEMS resonator, a method of manufacturing thereof, and a MEMS oscillator
The invention relates to a MEMS resonator comprising a movable element ( 48 ), the movable element ( 48 ) comprising a first part (A) having a first Young's modulus and a first temperature coefficient of the first Young's modulus, and the movable element ( 48 ) further comprising a second part (B) having a second Young's modulus and a second temperature coefficient of the second. Young's modulus, a sign of the second temperature coefficient being opposite to a sign of the first temperature coefficient, at least, at operating conditions of the MEMS resonator, and a cross-sectional area of the first part (A) and the cross-sectional area of the second part (B) being such that the absolute temperature coefficient of the Young's modulus of the first part (A) multiplied by the cross-sectional area of the first part (A) does not deviate more than 20% from the absolute temperature coefficient of the Young's modulus of the second part (B) multiplied by the cross-sectional area of the second part (B), the cross-sectional areas being measured locally and perpendicularly to the movable element ( 48 ).
1. A MEMS resonator comprising a movable element, the movable element comprising a first part having a first Young's modulus and a first temperature coefficient of the first Young's modulus, and the movable element further comprising a second part having a second Young's modulus and a second temperature coefficient of the second Young's modulus, a sign of the second temperature coefficient being opposite to a sign of the first temperature coefficient, at least, at operating conditions of the MEMS resonator, and a cross-sectional area of the first part and the cross-sectional area of the second part being such that the absolute temperature coefficient of the Young's modulus of the first part multiplied by the cross-sectional area of the first part does not deviate more than 20% from the absolute temperature coefficient of the Young's modulus of the second part multiplied by the cross-sectional area of the second part, the cross-sectional areas being measured locally and perpendicularly to the movable element.
2. A MEMS resonator as claimed in claim 1 , characterized in that a ratio of the cross-sectional area of the first part of the movable element divided by the cross-sectional area of the second part of the movable element approximately equals a further ratio of the negative temperature coefficient of the Young's modulus of the second part of the movable element divided by the temperature coefficient of the Young's modulus of the first part of the movable element.
3. A MEMS resonator according to claim 1 , characterized in that the first part or the second part comprises silicon and the other part comprises silicon oxide.
4. A method of manufacturing a MEMS resonator comprising the following steps:
providing a semiconductor body comprising a substrate layer, a sacrificial layer provided on the substrate layer, and a top layer provided on the sacrificial layer, the top layer comprising a first material for forming a first part of the movable element, the first part having a first Young's modulus and a first temperature coefficient of the first Young's modulus;
patterning the top layer for defining a movable element;
selectively removing the sacrificial layer for partially releasing the movable elementary from the substrate layer;
providing a second material onto the movable element for forming a second part of the movable element, the second part having a second Young's modulus and a second temperature coefficient of the second Young's modulus, the sign of the second temperature coefficient being opposite to the sign of the first temperature coefficient, at least, at operating conditions of the MEMS resonator, the cross-sectional area of the first part and the cross-sectional area of the second part being such that the absolute temperature coefficient of the Young's modulus of the first part multiplied by the cross-sectional area of the first part does not deviate more than 20% from the absolute temperature coefficient of the Young's modulus of the second part multiplied by the cross-sectional area of the second part, the cross-sectional areas being measured locally and perpendicularly to the movable element.
5. A method as claimed in claim 4 , characterized in that in the step of providing a semiconductor body, a top layer is provided on the sacrificial layer, which comprises silicon.
6. A method as claimed in claim 5 , characterized in that the step of providing the second material comprises an oxidation step, wherein at least the silicon of at least one sidewall of the movable element is converted into silicon oxide.
7. A MEMS oscillator comprising the MEMS resonator as claimed in claim 1 .
8. An integrated circuit comprising the MEMS oscillator as claimed in claim 7 .