Semiconductor filter circuit and method

• US 20030228848A1
• Filed: 06/11/2002
• Published: 12/11/2003
• Est. Priority Date: 06/11/2002
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Robb, Francine Y., Zdebel, Peter J., Stefanov, Evgueniy, Escoffier, Rene, Pearse, Jeffrey
• Granted Patent: US 6,953,980 B2
• Time in Patent Office: Days
• US Class Current: 455/91
• CPC Class Codes: H01L 27/0251 for MOS devices

Abstract

A filter circuit (10) is formed on a semiconductor substrate (11) formed with a trench (40) that is lined with a dielectric layer (38). A conductive material (37) is disposed in the trench and coupled to a node (62) to provide a capacitance that modifies a frequency response of an input signal (V_IN) to produce a filtered signal (V_OUT). An electrostatic discharge device includes an inductor (74) coupled to back to back diodes (17, 18) formed in the substrate to avalanche when a voltage on the node reaches a predetermined magnitude.

Claims

1. An integrated filter for filtering an input signal, comprising:

a substrate formed with a trench that is lined with a dielectric layer;

a first conductive material disposed in the trench and coupled to a node to provide a capacitance that modifies a frequency response of the input signal to produce a filtered signal; and

a protection circuit that includes back to back diodes formed in the substrate to avalanche when a voltage on the node reaches a predetermined magnitude.

2. The integrated filter of claim 1, wherein the protection circuit includes an inductor coupled to the back to back diodes.

3. The integrated filter of claim 2, wherein the inductor is formed as a planar device on a surface of the substrate.

4. The integrated filter of claim 1, wherein the substrate includes a base layer of a first conductivity type and a doping concentration in a range between 10¹⁸ and 10²¹ atoms per cubic centimeter.

5. The integrated filter of claim 4, wherein and the back to back diodes include:

a first doped region of a second conductivity type that forms a first junction with the base layer and; and

a second doped region having the first conductivity type for forming a second junction with the first doped region, wherein the second doped region is coupled to the node.

6. The integrated filter of claim 5, wherein the first doped region comprises an epitaxial layer grown on the base layer.

7. The integrated filter of claim 6, wherein the second doped region is diffused from a surface of the epitaxial layer.

8. The integrated filter of claim 7, wherein the second doped region includes:

a first portion having a first surface concentration and diffused to a first depth; and

a second portion having a second surface concentration less than the first surface concentration and diffused to a second depth greater than the first depth.

9. The integrated filter of claim 6, wherein the epitaxial layer includes:

a first portion formed over the base layer and having a first doping concentration; and

a second portion formed over the first portion and having a second doping concentration less than the first doping concentration.

10. The integrated filter of claim 6, wherein the epitaxial layer has a thickness between two and ten micrometers and a doping concentration in a range between 10¹⁶ and 10¹⁸ atoms per cubic centimeter.

11. The integrated filter of claim 6, wherein impurities of the first conductivity type are diffused through a surface of the epitaxial layer to reduce a doping concentration of the epitaxial layer within a depth less than three micrometers.

12. The integrated filter of claim 1, wherein the substrate includes a base layer having a doping concentration in a range between 10¹² and 10¹⁴ atoms per cubic centimeter.

13. The integrated filter of claim 1, wherein the trench is formed in a first well region of the substrate.

14. The integrated filter of claim 13, wherein the back to back diodes are formed in a second well region of the substrate, the second well region and substrate having the opposite conductivity type.

15. The integrated filter of claim 14, wherein the back to back diodes further comprise:

a first doped region formed within the second well region to provide a first junction of the back to back diodes; and

a second doped region formed within the second well region to provide a second junction of the back to back diodes.

16. The integrated filter of claim 1, wherein the first conductive material comprises doped polysilicon.

17. The integrated filter of claim 1, wherein the capacitance is produced by a trench capacitor, further comprising a thin film resistor coupled to the trench capacitor.

18. A wireless communications device, comprising:

a power stage that receives a modulated signal and transmits an output signal of the wireless communications device;

a modulator that modulates a radio frequency carrier signal with an audio signal to produce the modulated signal;

a microphone for converting voice information to the audio signal, where the microphone receives a portion of the output signal; and

a filter formed on a semiconductor substrate and interposed between the microphone and the power stage for attenuating radio frequency components of the output signal, including

a first conductive material disposed in a trench of the semiconductor substrate to provide a capacitance that attenuates the radio frequency components; and

an electrostatic discharge circuit including back to back diodes formed in the semiconductor substrate to limit an amplitude of a terminal voltage of the filter to a predetermined value.