Solid state RF switch with high cutoff frequency

• US 6,486,511 B1
• Filed: 08/30/2001
• Issued: 11/26/2002
• Est. Priority Date: 08/30/2001
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Clarke, R. Chris, Krafcsik, David M., Nathanson, Harvey C., Smith, Philip C., Dickens, Lawrence E.
• Primary Examiner(s): Flynn, Nathan J.
• Assistant Examiner(s): MANDALA, VICTOR A
• Application Number:
  US09/942,824
• Time in Patent Office: 453 Days
• Field of Search: 257/328, 257/329, 257/330, 257/331, 257/332, 257/401, 257/403, 257/135, 257/136
• US Class Current: 257/328
• CPC Class Codes: H01L 29/435 Resistive materials for field effect devices, e.g. resistive gate for MOSFET or MESFET
• CPC Class Codes: H01L 29/66666 Vertical transistors H01L29/66712, H01L29/66742 take precedence
• CPC Class Codes: H01L 29/7827 Vertical transistors H01L29/7802, H01L29/78642 take precedence

Abstract

A solid state microwave switch having a plurality of adjacent parallel fingers covered with an oxide layer. One end of a finger is an N+ source region while the other end is an N+ drain region, with a current conducting N region between them. The oxide layer is covered with a gate layer to which a gate signal is applied for control of current between the N+ regions through the N region. The gate layer is highly resistive and has a sheet resistance on the order of millions of ohms per square. The length from the source to drain region is around 2 μm, and the fingers are spaced with a pitch of around 1 μm.

Claims

1. An RF solid state switch, comprising:

(A) a plurality of adjacent semiconductor fingers each having first and second ends and an intermediate body portion, with one of said ends constituting a source region and the other of said ends constituting a drain region;

(B) each said finger having a width W, where W is less than around 5000 Å

;

(C) each said finger having an oxide layer on the surface thereof;

(D) each said finger having a resistive gate layer on said oxide layer;

(E) said resistive gate layer having a sheet resistance ρ

_g in the range of 100,000 to on the order of 5×

10⁶ ohms per square; and

(F) respective electrical contacts in electrical communication with said gate layer, and said source and drain regions.

2. A switch according to claim 1 wherein:

(A) said sheet resistance ρ

_g is at least 5×

10⁶ ohms per square.

3. A switch according to claim 1 wherein:

(A) said first and second ends, and said intermediate body portion are all of the same conductivity type, with said first and second ends having a higher doping concentration than said intermediate body portion.

4. A switch according to claim 1 wherein:

(A) the length of said intermediate body portion between said source and drain regions is on the order 2 μ

m.

5. A switch according to claim 1 wherein:

(A) the pitch of said adjacent semiconductor fingers is on the order of 1 μ

m.

6. A switch according to claim 1 wherein:

(A) the thickness of said oxide layer is on the order of 100 Å

to 1000 Å

.

7. A switch according to claim 1 wherein:

(A) the thickness of said gate layer is on the order of 100 Å

to 1000 Å

.

8. A switch according to claim 1 wherein:

(A) said semiconductor fingers are of silicon; and

(B) said gate layer is a polysilicon.

9. A switch according to claim 1 wherein:

(A) said fingers extend for a distance D; and

(B) said extended fingers are parallel to one another.

10. A switch according to claim 1 wherein:

(A) said switch is operated in the enhancement mode of operation whereby a positive gate voltage applied to said gate layer will turn said switch on.

11. An RF solid state switch, comprising:

(A) a plurality of adjacent vertical semiconductor fingers each having first, second and third layers with said first layer constituting one of a source or drain region and said third layer constituting the other of a source or drain region;

(B) said fingers extending from, and having a common one of said source or drain regions, so as to define fingers having distal ends, as well as horizontal interfinger portions;

(C) each said finger having a width W, where W is less than around 5000 Å

;

(D) each said finger having an oxide layer on the vertical surfaces thereof and in said horizontal interfinger portions;

(E) each said finger having a resistive gate layer on said oxide layer so as to extend along said vertical surfaces, as well as along said horizontal interfinger portions;

(F) said resistive gate layer which extends along said vertical surfaces having a sheet resistance μ

_g in the range of 100,000 to on the order of 5×

10⁶ ohms per square;

(G) said resistive gate layer which extends along said horizontal interfinger portions constitutes a gate pad having a sheet resistance lower than said resistive gate layer which extends along said vertical surfaces; and

(H) respective electrical contacts in electrical communication with said gate layer, and said source and drain regions.

12. A switch according to claim 11 wherein:

(A) said first, second and third layers are of the same conductivity type, with said first and third layers having higher doping concentrations than said second layer.

13. A switch according to claim 11 wherein:

(A) said resistive gate layer has a sheet resistance of at least 5×

10⁶ ohms per square; and

(B) said gate pad has a sheet resistance which is around 1000 times lower than that of said gate layer.

14. A switch according to claim 13 which includes:

(A) a gate pad contact, for application of a control signal, in electrical communication with said gate pad;

(B) said gate pad contact being metallic.

15. A switch according to claim 11 wherein:

(A) said distal ends of said fingers are in electrical communication with a common contact.