Sensor for measuring an ion concentration or gas concentration

• US 20020170824A1
• Filed: 04/12/2002
• Published: 11/21/2002
• Est. Priority Date: 04/12/2001
• Status: Active Grant

• Current Assignee: Tdk-Micronas Gmbh (TDK Corporation)
• Original Assignee: Micronas Gmbh (TDK Corporation)
• Inventors: Frerichs, Heinz-Peter
• Granted Patent: US 6,955,749 B2
• Time in Patent Office: Days
• US Class Current: 204/416
• CPC Class Codes: G01N 27/4143 Air gap between gate and channel, i.e. suspended gate [SG] FETs work function measurement per se G01N27/002
• CPC Class Codes: G01N 27/4148 Integrated circuits therefor, e.g. fabricated by CMOS processing CMOS processing per se H01L21/82
• 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

The invention relates to a sensor for measuring ion concentration or gas concentration, with a gas- or ion-sensitive layer (6) that has two sensitive partial areas (20 and 21), two conducting areas (1b and 2b), each coupled capacitively through air gaps (9and 10) with one of the sensitive partial areas (20 and 21), with the capacitances of the couplings being different, and a comparison circuit (1a, 2a, 3, 4, 5) which has at least one first transistor (T1) connected with the first conductive area and a second transistor (T2) connected with the second conductive area, and at least one output at which a signal can be tapped that depends on the potential of sensitive layer (6).

Claims

1. Sensor for measuring an ion concentration or a gas concentration with a sensitive layer (6) whose potential depends on a surrounding gas concentration or ion concentration, with the sensitive layer (6) having a first sensitive partial area (20) and a second sensitive partial area (21), a first conductive area (1b) that is capacitively coupled by a first air gap (9) with first sensitive partial area (20), a second conductive area (2b) coupled capacitively through a second air gap (10) with second sensitive partial area (21), with the capacitances of the two capacitive couplings being different, a comparison circuit (1a, 2a, 3, 4, 5) which has at least a first transistor (T1) connected with the first conducting area, and a second transistor (T2) connected with the second conducting area, and at least one output from which a signal can be tapped, depending on the potential of sensitive layer (6).

2. Sensor according to claim 1, characterized in that air gaps (9, 10) are of different sizes.

3. Sensor according to claim 2, characterized in that first conducting area (1b) is coupled capacitively by a first dielectric layer (7), preferably a first thick oxide layer, and second conductive area (2b) is connected by a second dielectric layer (8), preferably a second thick oxide layer, with a substrate (11).

4. Sensor according to claim 3, characterized in that first dielectric layer (7) is thicker than second dielectric layer (8) and first air gap (9) is smaller than second air gap (10).

5. Sensor according to claim 4, characterized in that the two sensitive partial areas (20, 21) are the same size and the two conductive areas (1b, 2b) are the same size.

6. Sensor according to claim 5, characterized in that the comparison circuit has at least a first and second field effect transistor (T1 and T2), preferably MOSFETs, on a common substrate (11), so that a first gate (1a) of the first field effect transistor is connected with the first conductive area (1b) and a second gate (2a) of the second field effect transistor is connected with second conductive area (2b).

7. Sensor according to claim 6, characterized in that the two transistors (T1 and T2) have a common source area (5).

8. Sensor according to claim 7, characterized in that first conductive area (1b) and first gate (1a) are made as a first conductive layer (1) and second conductive area (2b) and second gate (2a) are made as a second conductive layer (2).

9. Sensor according to claim 8, characterized in that first and second conductive layers (1, 2) are formed symmetrically, preferably in mirror symmetry to one another.

10. Sensor according to claim 9, characterized in that first and second air gaps (9, 10) are formed as partial areas of a chamber (22) formed beneath sensitive layer (6).

11. Sensor according to claim 10, characterized in that sensitive layer (6) is a gas-sensitive layer (6) and conducting areas (1b, 2b) are open to air gaps (9, 10).

12. Sensor according to claim 11, characterized in that sensitive layer (6) is an ion-sensitive layer (6), applied to an insulating layer (13, 14), which extends over first and second conducting areas (1b, 2b).

13. Sensor according to claim 12, characterized in that sensitive gate layer (6) and conducting areas (1b and 2b) are formed in a first section (17) of a substrate (11), and the comparison circuit is formed in a second section (18) of substrate (11) spaced lengthwise from first section (17).

14. Sensor according claim 13, characterized in that conductive layers (1 and 2) are poly layers or metal layers.

16. Method according to claim 15, characterized in that conductive layers (16) are located between intermediate layers (13 and 15).

15. Method for making a sensor, in which an insulating layer (7, 8), preferably a thick oxide layer, is formed on a substrate (11) of a first charge carrier type in a first section (17) and in a separate second section (18), separated lengthwise, at least two drain areas (3, 4) and a source area (5) of a second charge carrier type are formed preferably by ion implantation between which a thin oxide layer is applied, a first and second conductive layer (1, 2) are each applied to insulating layers (7, 8) and the thin oxide layer in such a way that two conductive areas (1b, 2b) are formed in the first section above the insulating layer and two gates (1a, 2a) are formed in a second section, at least two air gaps (9, 10) are formed between insulating intermediate layers (13, 15), and a sensitive layer (6) is applied to the intermediate layers in such a way that air gaps (9 and 10) are formed between two partial areas (20, 21) of sensitive layer (6) and conducting areas (1b and 2b).