Mesfet transistor with gate spaced above source electrode by layer of air or the like method of fabricating same

• US 4,807,002 A
• Filed: 05/26/1988
• Issued: 02/21/1989
• Est. Priority Date: 01/28/1985
• Status: Expired due to Fees

• Current Assignee: Alcatel Italia SpA (Nokia Corporation)
• Original Assignee: Telettra Telefonia Elettronica E Radio SPA
• Inventors: Donzelli, Giampiero
• Primary Examiner(s): James, Andrew J.
• Assistant Examiner(s): CLARK, SHEILA V
• Application Number:
  US07/201,353
• Time in Patent Office: 271 Days
• Field of Search: 357/23.1, 357/22 I, 357/22 H, 357/22 G, 357/22 E, 357/68, 357/67, 357/71, 357/69, 333/100, 333/136, 333/124, 333/128, 29/571
• US Class Current: 257/280
• CPC Class Codes: H01L 21/0271 comprising organic layers
• CPC Class Codes: H01L 21/28587 characterised by the sectional shape, e.g. T, inverted T
• CPC Class Codes: H01L 23/4821 Bridge structure with air gap
• CPC Class Codes: H01L 23/4824 Pads with extended contours, e.g. grid structure, branch structure, finger structure
• CPC Class Codes: H01L 29/42316 for field-effect transistors
• CPC Class Codes: H01L 29/475 on AIII-BV compounds
• CPC Class Codes: H01L 29/66863 Lateral single gate transistors
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: Y10S 148/142 Semiconductor-metal-semiconductor

Abstract

In a Schottky field effect MESFET transistor including a semiconductor substrate and source, gate and drain electrodes, the electrical resistance of the gate is reduced to substantially zero by implementing the gate electrode a sheet of metallization which bypasses a portion of the source electrode and which is spaced from the source electrode by a layer of air or the like. The MESFET transistor may be fabricated by providing drain and source electrodes as on a semiconductor substrate with the electrodes situated side-by-side. Photoresist is applied over at least the source electrode while leaving exposed (a) a first portion of the substrate surface between the source and drain electrodes and (b) a second portion of the substrate surface situated on an opposite side of the source electrode and which is used as a bonding pad location. Gate metallization is then formed over the photoresist and in contact with the first and second areas of the substrate surface. The metallization may also extend over the drain electrode that is later removed. Upon removal of the photoresist from between the gate and source electrodes, a layer of air of the like dielectrically separates these electrodes from each other. A portion of the gate metallization that overlies the drain electrode may exist as a tail that may have various lengths to make possible a non-critical patterning step for the gate metallization.

Claims

1. A metal-semiconductor field effect transistor comprising:

(a) a semiconductor substrate;

(b) elongated first and second electrodes contacting the substrate and spaced from each other by a first area of the substrate which has a length in the direction of elongation of said first and second electrodes; and

(c) a control electrode in sheet form, comprising;

(i) an elongated gate portion contacting the first area along at least a portion of the length of the first area;

(ii) a bonding pad portion contacting a second area of the substrate situated adjacent to the first electrode, and on the opposite side of the first electrode from the first area; and

(iii) a bridge portion bridging over the first electrode and having a first side adjoining the bonding pad portion and a second side adjoining the gate portion along substantially the entire portion of the length of the first area;

(d) whereby resistance of the control electrode is minimized.

2. A field effect transistor according to claim 1, wherein the bridge portion is spaced from the first electrode by a gaseous medium.

3. A field effect transistor according to claim 2, wherein the gaseous medium comprises air.

4. A field effect transistor according to claim 1, wherein the first electrode is generally "I"-shaped and includes an elongated longitudinally extending segment and a pair of heads respectively located at either end of the segment;

the control electrode having a longitudinal extent less than and a transverse extent much greater than the respective dimensions of the portion of the first electrode over which the control electrode passes.

5. A field effect transistor according to claim 1, wherein the second electrode has a longitudinal extent greater than that of the control electrode and a transverse extent of the same order of magnitude as the portion of the first electrode over which the control electrode passes.

6. A field effect transistor according to claim 1, wherein the side of the second electrode adjacent to the first area of the semiconductor surface is parallel to, and separated by a short distance from, the gate portion.

7. A field effect transistor according to claim 2, wherein the side of the second electrode adjacent to the first area of the semiconductor surface is parallel to, and separated by a short distance from, the gate portion.

8. A field effect transistor according to claim 1, wherein the second electrode has a bonding pad portion and the bonding pad portions of the control and second electrodes are centered on respective body portions, have areas of the same order of magnitude and are located at opposite sides of the device with respect to the elongated first electrode.

9. A field effect transistor according to claim 2, wherein the second electrode has a bonding pad portion and the bonding pad portions of the control and second electrodes are centered on respective body portions, have areas of the same order of magnitude and are located at opposite sides of the device with respect to the elongated first electrode.

10. The field effect transistor of claim 1, wherein the control electrode extends away from the first electrode in the form of a tail.

11. The field effect transistor of claim 2, wherein the control electrode extends away from the first electrode in the form of a tail.

12. The field effect transistor according to claim 1, wherein the first and second electrodes respectively comprise source and drain electrodes.