Ion sensitive field effect transistor (ISFET) sensor with improved gate configuration

• US 20050156584A1
• Filed: 01/20/2005
• Published: 07/21/2005
• Est. Priority Date: 01/21/2004
• Status: Abandoned Application

• Current Assignee: Rosemount Analytical, Inc. (Emerson Electric Company)
• Original Assignee: Rosemount Analytical, Inc. (Emerson Electric Company)
• Inventors: Feng, Chang-dong
• Application Number:
  US11/038,740
• Publication Number:
  US 20050156584A1
• Time in Patent Office: Days
• US Class Current: 324/71.500
• CPC Class Codes: G01N 27/414 Ion-sensitive or chemical field-effect transistors, i.e. ISFETS or CHEMFETS
• 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

Abstract

An ion sensitive field effect transistor pH sensor is provided with an improved sensor gate configuration. Specifically, a tantalum oxide-sensing gate is disposed on top of an alumina layer. The tantalum oxide-sensing gate provides advantageous sensitivity, while the alumina barrier layer increases sensor longevity in situations where the sensor is exposed to caustic cleaning processes such as Clean In Place processes.

Claims

1. An ion sensitive field effect transistor (ISFET) comprising:

a substrate having a sensing region;

a layer of silicon oxide (SiO₂) disposed over the sensing region of the substrate;

a barrier layer of alumina disposed over the layer of silicon oxide;

a tantalum oxide (Ta₂O₅) sensing membrane disposed over the barrier layer, and being configured for exposure to a solution.

2. The ISFET of claim 1, wherein the tantalum oxide sensing membrane has a thickness between about 100 and 5000 angstroms.

3. The ISFET of claim 1, wherein the silicon oxide layer is thermally grown on the substrate.

4. The ISFET of claim 1, wherein the ISFET is an npn ISFET.

5. The ISFET of claim 1, wherein the ISFET is a pnp ISFET.

6. A method of sensing ions with an ISFET, the method comprising:

contacting a tantalum oxide sensing membrane of the ISFET with a sample solution;

allowing ions in the sample solution to interact electrically with the sensing layer;

providing an alumina barrier layer proximate the sensing layer; and

measuring a drain current of the ISFET.