GB2156992A

GB2156992A - Proximity control switches

Info

Publication number: GB2156992A
Application number: GB08408375A
Authority: GB
Inventors: Jean-Francois Thomas
Original assignee: Glaverbel Belgium SA
Current assignee: AGC Glass Europe SA
Priority date: 1984-03-31
Filing date: 1984-03-31
Publication date: 1985-10-16
Also published as: GB8408375D0

Abstract

A proximity control switching key comprises, deposited on different faces of glass sheet material 1, 10, a floating command electrode 2 and two slave electrodes 13, 14 arranged in capacitive relation behind the command electrode 2. The key is transparent, and the electrodes 2, 13, 14 are formed by deposits of tin oxide. On at least one glass sheet face, the or each such electrode is deposited to a thickness in the range n x 100 to n x 130 nm, where n is 1 or 3. In a variant, at least one electrode-bearing glass sheet face bears dielectric material 3, 5 having a refractive index in the range 1.3 to 1.6 inclusive, such dielectric material being deposited to over-coat the or each electrode of that key on that sheet face to a thickness not exceeding 10 mu m. In another variant, the key comprises two slave electrodes 13, 14 formed by tin oxide deposited on different glass sheet faces and located in register with and at different distances behind the command electrode but out of register with each other, and each such sheet face bears an additional tin oxide deposit respectively 12, 11 in register with and of substantially the same size and thickness as each electrode 13, 14 on the respective other sheet face. <IMAGE>

Description

SPECIFICATION Proximity control switches This invention relates to a proximity control switching key constituted by electrodes deposited on different faces of glass sheet material, such key comprising a floating command electrode and two slave electrodes arranged in capacitive relation behind the command electrode. The invention also relates to keyboards incorporating such keys.

Keyboards incorporating such keys are well known, and their use for the control of many different kinds of equipment is increasing. Various constructions of such keys and keyboards are disclosed for example in British Patent Specifications Nos 2 060 895 and 2 061 004 to BFG Glassgroup, and in No 2 090 979 to Glaverbel.

There is, however, one potential field of use for such keyboards which requires certain properties not possessed by known keys, namely the use of such keyboards as facings for variable displays, for exam ple LED displays, which may for example be controlled by operation of the key or keys on the keyboard through which the display is to be viewed. In order that the display may be viewed without eye-strain caused for example by distracting reflective patterns across the keyborad, it is desirable that the visible light transmission properties of the keyboard over its area should conform to an acceptable criterion. It is an object of the present invention to provide a proximity control switching key for a keyboard which goes at least some way towards satisfying this objective.

According to the present invention, there is provided a proximity control switching key constituted by electrodes deposited on different faces of glass sheet material, such key comprising a floating command electrode and two slave electrodes arranged in capacitive relation behind the command electrode characterised in that the key is transparent, in that said electrodes are formed by deposits of tin oxide, and in that on at least one glass sheet face, the or each such electrode is deposited to a thickness in the range n x 100 to n x 130 nm, where n is 1 or 3.

The present invention enables the construction of a keyboard which may be placed in front of a display so that the display can be read through it. In general, tin oxide coatings have a refractive index of about 2, and this relatively high refractive index tends to give rather high reflection at the interface between the tin oxide coating and other material, for example the glass sheet on which it is deposited or air to which it is exposed. Light reflection by the or each electrode plate which satisfies the required thickness crite rion is reduced as compared with otherwise similar tin oxide electrode plates deposited to different thick nesses. Accordingly one or more such keys can be distributed across the keyboard in such a way as to give a less distracting reflecting pattern than has hitherto been possible.Tin oxide electrodes of such thicknesses have good optical and electrical properties for the purpose in view.

Further reduction of the difference in reflection as between the electrode-bearing portions of the glass sheet material and the remainder of the keyboard can be effected by adopting an additional feature which is particularly preferred, namely that at least one electrode-bearing glass sheet face bears dielectric material having refractive index in the range 1.3 to 1.6 inclusive, such dielectric material being deposited to over-coat the or each electrode of that key on that sheet face to a thickness not exceeding 10 Fm.

Tin oxide coatins generally have a refractive index index of about 2, as has been stated above. By overcoating those electrodes with a coating material having a refractive index approximately equal to the square root of the refractive index of tin oxide, it is found that the sum of the reflection at the tin oxide/ coating interface and the reflection at the coating/air interface is reduced as compared with the reflection at a tin oxide/air interface.

The adoption of this feature contributes to a reduction in the light reflected at the over-coated electrode, and gives an improvement in the uniformity of reflection from the keyboard even when the electrodes do not meet the thickness criterion set forth above.

Accordingly, in its second aspect, the present invention provides a proximity control switching key constituted by electrodes deposited on different faces of glass sheet material, such key comprising a floating command electrode and two slave electrodes arranged in capacitive relation behind the command electrode, characterised in that the key is transparent, in that said electrodes are formed by deposits of tin oxide, and in that at least one electrode-bearing glass sheet face bears dielectric material having a refractive index in the range 1.3 to 1.6 inclusive, such dielectric material being deposited to over-coat the or each electrode of that key on that sheet face to a thickness not exceeding 10 iim.

If only a single electrode is to be over-coated, the greatest benefit is obtained when the front electrode is over-coated, and it is accordingly preferred that at least the command electrode is so over-coated with said dielectric material. Optimally, each electrode of said key is so over-coated with a said dielectric coating.

A low difference in reflectivity as between the area of the key and surrounding areas of the glass sheet material is further promoted by adopting the preferred feature that the or each such dielectric over-coating has a thickness not exceeding 160 nm. The adoption of this feature contributes to interference extinction of light reflected by the over-coated electrode, and it has been found that a said dielectric coating having such a thickness is particularly beneficial in reducing light reflection from the area of an underlying tin oxide coating over a wide range of thicknesses of tin oxide coating and no matter what the num ber of glass sheets or their thickness.

It is especially preferred that the or at least one said dielectric coating be of silica. Silica coatings are hard and abrasion resistant, and can readily be formed to a thickness of for example 100nm with a refractive index of about 1.41 by a dipping technique using a solution of tetramethylorthosilicate in methanol, or by the pyrolysis of silicon hydride in the presence of oxygen.

The use of such a dielectric over-coating on tin oxide coated glazing material is described in British Patent Application No. 83 07 460, and the disclosure of that Application is specifically incorporated in this specification.

Preferred embodiments of the second aspect of this invention also conform to the first aspect of the invention, and accordingly it is preferred that on at least one glass sheet face, the or each such electrode is deposited to a thickness in the range n x 100 to n x 130nm, where n is 1 or 3.

A low difference in reflectivity as between the area of the key and surrounding areas of the glass sheet material is again promoted if at least the command electrode is deposited to a thickness in the said range n x 100 to n x 130nm, where n is 1 or 3, as is preferred.

For the same reason it is preferred that each electrode of said key is deposited to a thickness in the said range n x 100 to n x 130 nm, where n is 1 or 3, and the greatest benefit in respect of the thickness of the electrodes is achieved when n is 1 as is also preferred.

Keyboards are known in which each capacitor key comprises two slave electrodes formed by tin oxide deposited on different faces of dielectric sheet material and located in register with and at different distances behind the command electrode but out of register with each other. Such keyboards have the advantage of making it much easier to form connections between the slave electrodes and input or output terminals by depositing connector strips on the respective dieletric sheets.However such an arrangement is a further cause of differential reflection across the keyboard, and in order to reduce this phenomenon, it is preferred that said key comprises two slave electrodes formed by tin oxide deposited on different glass sheet faces and located in register with and at different distances behind the command electrode but out of register with each other, and that each such sheet face bears an additional tin oxide deposit in register with and of substantially the same size and thickness as each electrode on the respective other sheet face.

In fact in circumstances where a regular reflective pattern across a keyboard will not prove too distracting and can therefore by tolerated, this feature can give acceptable results no matter what the thickness of the tin oxide electrodes, and even when there is no dielectric coating over the electrodes.

Accordingly, in its third aspect, the present invention provides a proximity control switching key constituted by electrodes deposited on different faces of glass sheet material, such key comprising a floating command electrode and two slave electrodes arranged in capacitive relation behind the command electrode, characterised in that the keyboard is transparent, in that said electrodes are formed by deposits of tin oxide, in that said key comprises two slave electrodes formed by tin oxide deposited on different glass sheet faces and located in register with and at different distances behind the command electrode but out of register with each other, and in that each such sheet face bears an additional tin oxide deposit in register with and of substantially the same size and thickness as each electrode on the respective other sheet face.

In some preferred embodiments of the invention, the rearmost additional tin oxide deposit is connected to an earth terminal. This can provide a measure of shielding against electric fields generated by any apparatus located behind a keyboard bearing such a key.

Advantageously, the front slave electrode of said key has a lesser area than the rear slave electrode of that key. The adoption of this preferred feature enables the capacitances of the two capacitors formed by those slave electrodes and the floating command electrode to be equalised, in turn giving advantages in electronic control. This feature is of considerable practical importance, and its adoption is further described in our copending British Patent Application No. 84 08376 (Publication No. GB A) of even date herewith filed under agents' reference 394 DUALKEY, and the disclosure of that Application is specifically incorporated in this specification.

The glass sheet material used may be chemically tempered, and the or each such glass sheet preferably has a thickness of 1.5mm or less.

Advantageously, the or each such electrode-bearing glass sheet has been subjected to a dealkalising treatment. It has been found that a tin oxide coating having good maechanical and optical properties can more easily be obtained on a sheet of glass which has a low sodium content at least at its surface, and that when applied to such a sheet, the tin oxide coating is more adherent, so prolonging the useful life of the product. The adoption of this feature is also beneficial for giving a product having a relatively low diffuse transmission of light over the areas coated with tin oxide.

The present invention includes a keyboard for a proximity control switching panel including a plurality of switching keys deposited in common on one or more sheets of glass, characterised in that at least some of said keys are keys according to the invention as herein defined.

It is not essential that all the keys on such a keyboard should be as herein defined. For example it might be desirable that some of the keys should be highly reflective in order to show their position on the keyboard. However in preferred embodiments of keyboard according to the invention, all said keys are keys according to the invention as herein defined.

The present invention will now be described in greater detail by way of example only, with reference to the accompanying diagrammatic drawings, in which Figures 1 to 6 are cross sectional views of six different embodiments of keyboard incorporating keys according to the invention.

In the drawings, a keyboard comprises a transparent glass sheet 1, preferably of dealkalised glass, on the front face of which, shown as the upper face, is deposited a plurality of floating command electrodes 2 of tin oxide. Glass may be dealkalised by exposing it to an atmosphere containing an acid gas such as SO3, which can be formed in situ by passing SO2 over a suitable catalyst to reduce handling problems.

As an alternative, dealkalisation can be effected by spraying the glass with a solution of HCI. The glass is preferably less than 1.5mm thick, and may for example be between 1.0mum and 0.4mm thick. In the embodiment of Figure 1, those command electrodes 2 have a thickness in the range n x 100 to n x 130 nm, where n is 1 or 3 (preferably 1), for example a thickness of 114nm, and the command electrodes 2 shown in the remaining Figures preferably have a like thickness.

In the embodiments of Figures 2, 3 and 6, these front facing command electrodes 2 are over-coated by a light transmitting dielectric coating 3. In the embodiment of Figure 2, and preferably in the embodiments of Figures 3 and 6, such dielectric coating 3 has a refractive index in the range 1.3 to 1.6 and a thickness not exceeding 10 Fm. In fact the coatings 3 preferably each have a thickness not exceeding 160 nm, for example a thickness of 95 nm. Such a coating increases the luminous transmissivity of the electrode and its substrate. Such a dielectric coating may also be applied to the keyboards shown in Figures 1, 4 and 5.

In the embodiments of Figures 1, 2 and 3, the glass sheet 1 bears a pair of slave electrodes 4 arranged in capacitive relation behind each command electrode 2. The slave electrodes 4 are also formed by tin oxide deposits, and they preferably have a thickness in the range n x 100 to n ts 130 nm, where n is 1 or 3 (preferably 1), for example a thickness of 114nm.

In the embodiment of Figure 3, a light transmitting dielectric coating 5 is applied to the rear face of the glass sheet 1 to cover the slave electrodes 4. This second dielectric coating 5 suitably has properties substantially identical to those of the dielectric coating 3 applied to the front face of that sheet.

In the embodiment shown in Figure 4, there are no slave electrodes 4 applied to the rear face of the glass sheet 1 which bears the command electrodes 2, rather each capacitor key comprises two slave electrodes 6,7 formed by tin oxide deposited on different faces 8,9 of a second glass sheet 10 which electrodes are located in register with and at different distances behind the command electrode 2 but out of register with each other. Furthermore, each such sheet face 8,9 bears additional tin oxide deposits respectively 11,12 in register with and of substantially the same size and thickness as respective slave electrodes 7,6 on the respective other sheet face. Again, each such slave electrode 6,7 and each such additional tin oxide deposit 11,12 preferably has a thickness in the range from n x 100 to n x 130 nm, where n is 1 or 3 (preferably 1), for example a thickness of 114nm.The additional tin oxide deposits 12 on the rearmost sheet face 9 are preferably connected to one or more earth terminals, for example they may form part of a continuous conductive pattern which is provided with a pair of terminals for connection to earth.

In the embodiment of Figure 4, it may be inferred from the drawing that the slave electrodes 6,7 are of substantially the same size. Because these electrodes are located at different distances behind the floating command electrodes 2, this would lead to the capacitors formed by the electrode pairs 2,6 and 2,7 having different capacitances, and this can give rise to difficulties in constructing a suitable monitoring circuit. This problem can be overcome by making the front slave electrode of smaller area than the rear slave electrode as shown in Figures 5 and 6.

In the embodiment shown in Figure 5, there is likewise provided a second glass sheet 10, and each capacitor key comprises two slave electrodes 13,14 formed by conductive tin oxide deposited on different faces 8,9 of the glass sheet 10. As in the embodiment of Figure 4, these slave electrodes 13,14 are located in register with and at different distances behind respective command electrodes 2 but out of register with each other. However, in the embodiment of Figure 5, the front slave electrode 13 has a lesser area than the rear slave electrode 14. Both slave electrodes 13,14 illustrated in Figure 5 are formed by tin oxide deposits, and preferably to a thickness in the range n x 100 to n x 130 nm, where n is 1 or 3 (preferably 1), for example of thickness of 114nm.

Figure 6 shows a further embodiment of the present invention in which slave electrodes 13,14 of different areas are deposited on different faces of a second glass sheet 10, and in which additional tin oxide deposits 11,12 respectively equal in area to the slave electrodes 14,13 are deposited in register with those electrodes on the same sheet face as the respective other slave electrodes 13,14. The front facing command electrodes 2 are over-coated by a light transmitting dielectric coating 3 which preferably has a refractive index in the range 1.3 to 1.6 and a thickness not exceeding 10 slum. As with the embodiment of Figure 3, a light transmitting dielectric coating 5 is applied to the rear face of the glass sheet 10 to cover the slave electrodes 14 and the additional tin oxide deposits 12. This second dielectric coating 5 suitably has properties substantially identical to those of the dielectric coating 3 applied to the front face of the sheet 1. These dielectric coating are suitably of silica.

Tin oxide electrodes or additional deposits may readily be formed in situ on glass sheet by pyrolysis of a solution of tin tetrachloride in DMF which contains trifiuoroacetic acid to give a fluorine doped tin oxide whose thickness can readily be controlled to within 12nm of 114nm and which has a resistivity within the range 45 to 60 Ohms per square. The pattern of the tin oxide deposit thus obtained can be controlled to define electrodes, any required additional tin oxide deposits and any required connectors by previously applying a mask to the substrate to be coated using a serigraphic technique.

A dielectric over-coating of silica, which is an especially suitable material to use in view of its hardness and in particular its refractive index, can readily be applied to both sides of a glass sheet bearing electrode deposits by a dipping technique, using a solution of the following composition: Tetramethylorthosilicate Si(OCH3)4 0.55 mole Water 0.75 mL HC1 1.0 mL Methanol to 1.0 L.

Before or after removal of the serigraphic mask, but preferably after, the sheet is dipped into such a solution and withdrawn steadily. The thickness of the coating can be regulated by varying the speed of withdrawal. The dipped glass is then heated in air to as high a temperature as is convenient, for example to a temperature in the range 500"C to 600"C to convert the Si(OCH3)4 in turn to Si(OH)4 and finally to SiO2. A silica layer having a thickness of 95 nm and a refractive index of about 1.41 as is particularly preferred, can easily be formed in this way.

As an indication of the benefits afforded by depositing tin oxide electrodes to the optimum thickness of 114 nm, comparison may be made between the reflectivity of areas occupied by keys incorporating such electrodes, of surrounding areas of keyboard, and of other areas occupied by keys whose electrodes are deposited to a different thickness, for example between 10 and 20 nm, on an otherwise similar keyboard.

Considering a keyboard comprising two sheets of glass, the areas occupied by keys having electrodes with a thickness in the range 10 to 20 nm had a reflectivity of 28 per cent. The areas occupied by keys having electrodes with a thickness of about 114 nm had a reflectivity of 20 per cent. Surrounding keyboard areas had a reflectivity of 16 per cent. An appreciable reduction in the difference between the reflectivity of the areas of the keys and surrounding areas of the keyboard is afforded by over-coating the faces of the glass bearing the electrodes with a 95 nm thick coating of silica which has a refractive index of about 1.41. This augments the light transmissivity of the keys. Similarly advantageous results are achieved when the keyboard comprises but one glass sheet.

Claims

1. A proximity control switching key constituted by electrodes deposited on different faces of glass sheet material, such key comprising a floating command electrode and two slave electrodes arranged in capacitive relation behind the cornmand electrode, characterised in that the key is transparent, in that said electrodes are formed by deposits of tin oxide, and in that on at least one glass sheet face, the or each such electrode is deposited to a thickness in the range n x 100 to n x 130 nm, where n is 1 or 3.

2. A key according to claim 1, wherein at least one electrode-bearing glass sheet face bears dielectric material having a refractive index in the range 1.3 to 1.6 inclusive, such dielectric material being deposited to over-coat the or each electrode of that key on that sheet face to a thickness not exceeding 10 ijm.

3. A proximity control switching key constituted by electrodes deposited on different faces of glass sheet material, such key comprising a floating command electrode and two slave electrodes arranged in capacitive relation behind the command electrode, characterised in that the key is transparent, in that said electrodes are formed by deposits of tin oxide, and in that at least one electrode-bearing glass sheet face bears dielectric material having a refractive index in the range 1.3 to 1.6 inclusive, such dielectric material being deposited to over-coat the or each electrode of that key on that sheet face to a thickness not exceeding 10 Fm.

4. A key according to claim 2 or 3, wherein at least the command electrode is so over-coated with said dielectric material.

5. A key according to claim 4, wherein each electrode of said key is so over-coated with a said dielectric coating.

6. A key according to any of claims 2 to 5, wherein the or each such dielectric over-coating has a thickness not exceeding 160 nm.

7. A key according to any of claims 2 to 6, wherein the or at least one such dielectric over-coating is of silica.

8. A key according to any of claims 3 to 7, wherein on at least one glass sheet face, the or each such electrode is deposited to a thickness in the range n x 100 to n x 130 nm, where n is 1 or 3.

9. A key according to claim 1, 2 or 8, wherein at least the command electrode is deposited to a thickness in the said range n x 100 to n x 130 nm, where n is 1 or 3.

10. A key according to claim 9, wherein each electrode of said key is deposited to a thickness in the said range n x 100 to n x 130 nm, where n is 1 or 3.

11. A key according to any of claims 1, 2, 8, 9 and 10, wherein n is 1.

12. A key according to any preceding claim, wherein said key comprises two slave electrodes formed by tin oxide deposited on different glass sheet faces and located in register with and at different distances behind the command electrode but out of register with each other, and wherein each such sheet face bears additional tin oxide deposit in register with and of substantially the same size and thickness as each electrode on the respective other sheet face.

13. A proximity control switching key constituted by electrodes deposited on different faces of glass sheet material, such key comprising a floating command electrode and two slave electrodes arranged in capacitive relation behind the command electrode, characterised in that the keyboard is transparent, in that said electrodes are formed by deposits of tin oxide, in that said key comprises two slave electrodes formed by tin oxide deposited on different glass sheet faces and located in register with and at different distances behind the command electrode but out of register with each other, and in that each such sheet face bears an additional tin oxide deposit in register with and of substantially the same size and thickness as each electrode on the respective other sheet face.

14. A key according to claim 12 or 13, wherein the rearmost additional tin oxide deposit is connected to an earth terminal.

15. A key according to claim 12, 13 or 14 wherein the front slave electrode of said key has a lesser area than the rear slave electrode of that key.

16. A key according to any preceding claim, wherein the or each such glass sheet has a thickness of 1.5 mm or less.

17. A key according to any preceding claim, wherein the or each such electrode-bearing glass sheet has been subjected to a dealkalising treatment.

18. A keyboard for a proximity control switching panel including a plurality of switching keys deposited in common on one or more sheets of glass, characterised in that at least some of said keys are keys according to any preceding claim.

19. A keyboard according to claim 18, wherein all its keys are keys according to any of claims 1 to 17.