Selection of materials and dimensions for a micro-electromechanical switch for use in the RF regime

• US 20020195681A1
• Filed: 04/17/2001
• Published: 12/26/2002
• Est. Priority Date: 04/17/2001
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Williams, Byron, Crenshaw, Darius, Chen, Yu-Pei, Melendez, Jose L.
• Granted Patent: US 6,525,396 B2
• Time in Patent Office: Days
• US Class Current: 257/528
• CPC Class Codes: H01G 5/16 using variation of distance between electrodes
• CPC Class Codes: H01G 5/40 Structural combinations of variable capacitors with other electric elements not covered by this subclass, the structure mainly consisting of a capacitor, e.g. RC combinations
• CPC Class Codes: H01H 59/0009 making use of micromechanics

Abstract

The present invention provides an apparatus and method of selecting a unique combination of materials and dimensions for fabrication of a micro-electromechanical switch for improved RF switch performance. An electrode material is selected which exhibits a resistivity resulting in improved insertion loss for a predetermined switching speed, a dielectric material is selected which exhibits a permittivity resulting in improved isolation, and an airgap thickness is selected resulting in a pull-down voltage approximately equal to a supply voltage of the micro-electromechanical switch in which the isolation and predetermined switching speed are also functions of the airgap thickness.

Claims

1. A method of selecting a combination of materials and dimensions for fabrication of a micro-electromechanical switch for improved RF switch performance, comprising the steps of:

selecting an electrode material exhibiting a resistivity resulting in improved insertion loss performance for a predetermined switching speed of said micro-electromechanical switch, wherein said insertion loss is a function of resistivity;

selecting a dielectric material for said micro-electromechanical switch exhibiting a permittivity resulting in improved isolation performance for said predetermined switching speed, wherein said isolation is a function of permittivity; and

selecting an airgap thickness resulting in a pull-down voltage approximately equal to a supply voltage of said micro-electromechancial switch for said pre-determined switching speed.

2. The method of claim 1, wherein said insertion loss is defined by:

3. The method of claim 1, wherein said isolation is defined by:

4. The method of claim 1, wherein said pull-down voltage is defined by:

5. The method of claim 1, wherein said predetermined switching speed is defined by:

6. The method of claim 1, wherein said acts of selecting an electrode material, dielectric material, and airgap thickness is performed in a software application.

7. The method of claim 1, wherein said isolation, pull-down voltage and predetermined switching speed are all functions of said airgap thickness.

8. A micro-electromechanical switch fabricated with a unique combination of materials and dimension for improved RF switch performance, comprising:

electrode fabricated from a determined electrode material exhibiting a resistivity resulting in improved insertion loss performance for a predetermined switching speed;

dielectric contact fabricated from a determined dielectric material exhibiting a permittivity resulting in improved isolation performance for said predetermined switching speed; and

airgap thickness fabricated into said micro-electromechanical switch, said airgap thickness determined to result in a pull-down voltage approximately equal to a supply voltage of said micro-electromechanical switch.

9. The micro-electromechanical switch of claim 8, wherein insertion loss is defined by:

10. The micro-electromechanical switch of claim 9, wherein said isolation is defined by:

11. The micro-electromechancial switch of claim 8, wherein said pull-down voltage is defined by:

12. The micro-electromechanical switch of claim 8, wherein said predetermined switching speed is defined by:

13. The micro-electromechanical switch of claim 8, wherein said electrode material, dielectric material and airgap are determined from a software application.

14. The micro-electromechanical switch of claim 8, wherein said isolation, pull-down voltage, and predetermined switching speed are all functions of said determined airgap thickness.

16. The method of claim 15 wherein said predetermined switching speed is defined by:

17. The method of claim 15 wherein said acts of selecting an electrode material, dielectric material and airgap thickness is performed in a software application.

15. A method of selecting a unique combination of materials and dimensions for fabrication of a micro-electromechancial switch for improved RF switch performance, comprising the steps of:

selecting an electrode material exhibiting a resistivity resulting in improved insertion loss performance for a predetermined switching speed of said micro-electromechanical switch, wherein said insertion loss is a function of resistivity;

wherein said insertion loss is defined by;

$\mathrm{InsertionLoss}\propto <br><br>10<br><br>\mathrm{Log}<br><br>\left[\frac{R_{\mathrm{transmissionline}}+R_{\mathrm{electrode}}}{R_{\mathrm{transmissionline}}}\right],$

 

wherein R_electrode represents a resistance of said electrode material and wherein R_{transmission line} represents a resistance of a corresponding transmission line;

selecting a dielectric material for said micro-electromechanical switch exhibiting a permittivity resulting in improved isolation performance for said predetermined switching speed, wherein said isolation is a function of permittivity, wherein said isolation is defined by;

$\mathrm{Isolation}\propto <br><br>10<br><br>\mathrm{Log}<br><br>\left[\frac{C_{\mathrm{on}}}{C_{\mathrm{off}}}\right]=10<br><br>\mathrm{Log}<br><br>\left[1+\frac{{\mathrm{\varepsilon <br><br>}}_{\mathrm{die}}<br><br>D_{\mathrm{air}}}{{\mathrm{\varepsilon <br><br>}}_{\mathrm{air}}<br><br>D_{\mathrm{die}}}\right],$

 

wherein C_on/C_off is a ratio of on to off capacitance, ε

_die is a permittivity of said dielectric material, ε

_air is a dielectric constant of said airgap, D_die is a measure of the thickness of said dielectric material, and D_air is a measure of the thickness of said airgap; and

selecting an airgap thickness resulting in a pull-down voltage approximately equal to a supply voltage of said micro-electromechancial switch for said pre-determined switching speed, wherein said pull-down voltage is defined by;

$V_p=\sqrt{\frac{8<br><br>{K<br><br>\left(g_0+P/K\right)}^3}{27<br><br>{\mathrm{\varepsilon <br><br>}}_{\mathrm{air}}}},$

 

wherein g₀ is a zero voltage distance of a membrane electrode to a bottom electrode/dielectric surface, P is the load on said membrane electrode, ε

_air is a dielectric constant of said airgap, and K is defined by;

$\frac{16<br><br>{\mathrm{Et}}^3}{3<br><br>a^4<br><br>\left(1-v^2\right)}+\frac{4<br><br>\mathrm{\sigma <br><br>t}}{a^2},$

 

wherein E is Young'"'"'s modulus, t is a measure of a thickness of said membrane electrode, ν

is Poisson'"'"'s ratio, σ

is a residual biaxial stress in said membrane electrode, and α

is a s of said membrane electrode.