Capacitive humidity sensor and method for the manufacture of same

• US 4,500,940 A
• Filed: 12/19/1983
• Issued: 02/19/1985
• Est. Priority Date: 12/21/1982
• Status: Expired due to Fees

• Current Assignee: Vaisala OY
• Original Assignee: Vaisala OY
• Inventors: Lehto, Ari, Kuisma, Heikki T., Jalava, Jouko S.
• Primary Examiner(s): Griffin, Donald A.
• Application Number:
  US06/562,746
• Time in Patent Office: 428 Days
• Field of Search: 361/286, 338/35, 174/52 FP, 73/335, 73/336, 73/336.5
• US Class Current: 361/286
• CPC Class Codes: G01N 27/225 by using hygroscopic materials

Abstract

The present publication describes a capacitive humidity sensor and a method for the manufacture of same. The sensor comprises a substrate (1), first (5) and second bottom electrodes (4), which have been fitted close to each other on the substrate (1), an active layer (7), which fills the area between the first (5) and the second bottom electrodes (4) on the substrate (1) and extends to above the top face of the second electrode (4). According to the invention, the sensor further consists of structures (6) connected to the top face of the first electrode (5), made of a conductive material, and being beam-shaped with an upwardly widening section and being placed side by side, the said structures (6) limiting portions (7) of the active layer between themselves from two sides, and a narrow slot (26) being provided between the top faces of the said structures. Owing to its construction, the sensor is not sensitive to touching.

Claims

1. Capacitive humidity sensor, which comprises

a substrate made, e.g., of glass,

at least one first and one second bottom electrode arranged close to each other on the substrate,

an active layer, which fills the area between the first and the second bottom electrode on the substrate and extends to above the top face of the second electrode,

a plurality of conductive, beam-shaped structures placed side by side, connected to the first electrode, and having an upwardly widening cross-section, said structures limiting portions of the active layer between themselves from two sides such that a narrow slot is formed between the top faces of said structures.

2. Humidity sensor as claimed in claim 1, wherein the beam-shaped structures are at least substantially of a trapezoidal cross-sectional form.

3. Humidity sensor as claimed in claim 1, wherein the beam-shaped structures are at least substantially of a T-shaped cross-sectional form.

4. Humidity sensor as claimed in claim 1, wherein the beam-shaped structures are made of silicon.

5. Humidity sensor as claimed in claim 1, wherein the beam-shaped structures are made of a metal.

6. Method for the manufacture of a capacitive humidity sensor as claimed in claim 1, comprising:

(a) depositing an epitactic layer weakly doped with boron onto a silicon disc or equivalent,

(b) doping the surface of the layer strongly with boron so as to form a surface layer,

(c) patterning, e.g., photolithographically, into this surface layer such oblong areas as are to be retained,

(d) etching off by means of an appropriate etching agent, e.g. KOH, the areas between the desired areas so that adjoining ridges projecting outwards from the silicon disc are formed,

(e) depositing onto a substrate, e.g., a glass substrate, at least one first and one second electrode layer as thin metal films,

(f) fitting the substrate and the silicon disc against each other so that the ridges and the first electrode reach contact with each other, and joining them together in a way known per se,

(g) etching off the silicon disc by means of an etching agent which etches the strongly doped silicon material such that only the ridges remain as beam-shaped structures,

(h) submerging the construction in this way obtained into a solution of an active isolating material sensitive to humidity, e.g., a polymer, and allowing this solution to penetrate into the space between the beams, and

(i) lifting off the construction out of the solution, and allowing the solvent to evaporate, whereby a solid active isolator material remains in the space between the beams.