GB2506347B

GB2506347B - Method for Forming an Electrode Structure for a Capacitive Touch Sensor

Info

Publication number: GB2506347B
Application number: GB1216357.2A
Authority: GB
Inventors: Prieto Rio Camilo; Kwan Chan Yuk
Original assignee: M Solv Ltd
Current assignee: M Solv Ltd
Priority date: 2012-09-13
Filing date: 2012-09-13
Publication date: 2019-07-10
Anticipated expiration: 2032-09-13
Also published as: GB2506347A; GB201216357D0

Description

Method for forming an electrode structure for a capacitive touch sensor

This invention relates to a method of forming an electrode structure for a capacitive touch sensor.

Background: There is a requirement to incorporate capacitive touch sensors into devices such as smart phones, MP3 players, PDAs, tablets, Ultrabook PCs, AIO PCs, etc. Such devices generally have a front transparent cover that is made of glass or plastic onto the rear of which a transparent capacitive sensor is bonded. The capacitive sensor often consists of a substrate made from a transparent material such as plastic or glass on opposite sides of which transparent conductive (TC) materials such as indium tin oxide (ITO) are applied and patterned to form transmit electrode (Tx) and receive electrode (Rx) layers. Alternatively a single layer sensor can be used which consists of one TC layer applied to the substrate which is suitably patterned and interconnected to form separately addressable Tx and Rx structures.

The cover/touch sensor assembly is attached to the display module which typically consists of a liquid crystal display (LCD). Such an arrangement leads to a cover/sensor /display module that is undesirably thick and heavy. To reduce the thickness and weight it is desirable to form the capacitive touch sensor directly on the cover or integrate the touch sensor into the LCD in some way.

Sensors that are integrated into LCDs can be of two types: "on-cell" type and "incell type". In the on-cell type a single TC layer is deposited on top of an organic planarization layer on top of an RGB (red-green-blue) colour filter (CF) and is patterned and interconnected to form both the Tx and Rx structures. In the incell type two separate TC layers are used: one for the Tx layer and one for the Rx layer. The two layers are situated either on each side of the RGB CF or both layers are placed below the RGB CF. In the former case the TC layer is deposited on top of an organic planarization layer on top of the RGB CF and is patterned to form the Rx structure. Hence for both on-cell and in-cell sensors there are situations where it is necessary to form a pattern in a TC layer situated on top of an organic layer on top of an RGB CF. The present invention seeks to provide an improved method for forming an electrode structure in this TC layer.

Summary of Invention

According to an aspect of the invention, there is provided a method of forming an electrode structure for a capacitive touch sensor in a transparent conductive layer located on a transparent non-conductive layer which is located on a colour filter layer, wherein: the method comprises forming the electrode structure using a pulsed laser to apply a direct write laser scribing process using to form grooves in the transparent conductive layer to electrically isolate areas of the transparent conductive layer on opposite sides of each groove while the transparent conductive layer located on the transparent non-conductive layer which is located on the colour filter layer, the laser wavelength and pulse length being selected from one of the following: a. a wavelength in the range lOlOnm to 1560nm and a pulse length of 80ps or less, and b. a wavelength in the range 340nm to 355nm and a pulse length of 80ps or less.

Other preferred and optional features of the invention will be apparent from the following description and the subsidiary claims of the specification.

Brief Description of Drawings

The invention will now be further described, merely by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of a known on-cell capacitive touch sensor module;

Figure 2 is a sectional view of a known in-cell capacitive touch sensor module;

Figure 3 illustrates formation of a groove in a transparent conductive layer of an on-cell module such as that shown in Figure 1; and

Figure 4 is a schematic perspective view of apparatus for carrying out the method illustrated in Figure 3.

Description of illustrated embodiments

Figure 1: This shows the construction of an on-cell capacitive touch sensor module. A transparent substrate 1 which is typically made of glass or plastic has an RGB colour filter (CF) 2 formed on a first side thereof. The CF consists of alternate stripes 3, 3', 3"or a two-dimensional array of localized areas of RGB materials corresponding respectively to the lines of or individual pixels in an LCD. A multi-step lithographic process is typically used to form such an RGB structure. A thin transparent non conducting layer 4 is applied to the top side of the CF to form a smooth upper surface. An organic material such as polymethylmethacrylate (PMMA) or acrylic is typically used to form this layer. A TC layer 5 is deposited on top of the organic layer 4. After suitable lithographic patterning and interconnection, the TC layer 5 becomes both the Tx and Rx electrodes of a single layer capacitive touch sensor. The sensor/CF assembly is then aligned to and attached to an LCD (not shown) with the TC layer on top and a polarizer layer (not shown) added to complete the LCD/CF/sensor assembly.

Figure 2: This shows the construction of one type of in-cell capacitive touch sensor module where the Rx layer is situated above the RGB CF. The structure and method of manufacture is similar to that of the one layer on-cell sensor shown in figure 1 with the difference that the TC layer 5, deposited on top of the organic layer 4, after lithographic patterning becomes only one electrode (Rx) of the two layer sensor. Another TC layer 6, is deposited on the rear side of the assembly to form (after lithographic patterning) the other (Tx) electrode of the two layer capacitive touch sensor. The sensor/CF assembly is then aligned to and attached to an LCD (not shown) with the Rx layer on top and a polarizer layer (not shown) added to complete the LCD/CF/sensor assembly.

Figure 3: This illustrates a method for forming a pattern in the TC layer 5 on top of the organic layer 4 on the CF. A laser beam 7 is focussed on the surface of topside TC layer 5 and moved over the surface so as to remove material by laser ablation to form a pattern of grooves 8 in the TC layer 5. The laser beam 7 removes all TC material in the grooves 8 so that there is no electrical conduction across the groove 8 but it causes no damage to the organic layer 4 or the RGB layer 2 in terms of their function.

The laser used is of pulsed type emitting pulses with duration less than 80ps and preferably less than 30ps. Lasers emitting pulses with sub ps duration are also suitable, eg 800fs or less. Laser operation can be in the infra-red (IR) range or in the ultra-violet (UV) range. IR and UV wavelengths are preferred since the TC layer 5 has some small but finite absorption in these wavelength regions. Operation in the visible region (510nm to 532nm) is not desirable as the TC layer has minimal absorption and parts of the RGB CF have significant absorption at this wavelength.

The laser used is selected from one of the following: an IR laser having a wavelength in the range 1030nm to 1560nm may be used with a pulse length of 80ps or less, and a UV laser having a wavelength in the range 340nm to 355nm and a pulse length of 80ps or less.

Pulse lengths in the range 80 to 10 ps or in the range 30 to 10 ps are preferred. The IR laser may, for example, be one of the following: A laser with a wavelength of 1030nm and a nominal pulse length of 30ps, A laser with a wavelength in the range 1010 to 1070nm and a nominal pulse length of 70ps, A laser with a wavelength of 1064nm and a nominal pulse length of 15ps or A laser with a wavelength of 1552nm and a nominal pulse length of 800fs

The preferred wavelength for an IR laser is in the range 1030nm to 1064nm and the preferred pulse length is 30ps or less.

The UV laser may, for example, be one of the following: A laser with a wavelength of 343nm and a nominal pulse length of 50ps, A laser with a wavelength of 355nm and a nominal pulse length of 15ps or A laser with a wavelength of 355nm and a nominal pulse length of lOps

It is found that UV and IR lasers with a pulse length in the 10ns to 200ns range are not suitable as damage to the underlying CF materials occurs. However, if a shorter pulse length is used, ie 80ps or less, satisfactory results are achievable.

Shorter pulse lengths are generally preferred as the TC layer and the underlying organic layer can be very thin, eg 100 nm or less, so are susceptible to thermal damage. The shorter the pulse length, the shorter the time period in which heat energy from the laser pulse can diffuse into adjacent areas.

It will be appreciated that the laser wavelength and pulse length are selected such that the laser scribing process forms grooves in the transparent conductive layer that electrically isolate areas of the transparent conductive layer on opposite sides of each groove and that this needs to be done with substantially no damage to the transparent non-conductive layer or the colour filter layer beneath the transparent conductive layer. By this means, a series of grooves can be formed in the transparent conductive layer to form an electrode structure therein. The grooves typically have a width in the range 5 to 30pm though wider grooves are also possible.

Figure 4: This shows a schematic perspective view of one form of apparatus arranged to carry out the laser patterning process described above. Laser 9 emits laser beam 10 which is directed via mirrors 11, 11' to a two-dimensional scanner unit 12. The beam exiting the scanner 12 is focussed by an f-theta lens 13 onto the surface of a substrate 14 which is mounted on stages such that it can be moved in directions X and Y. The substrate 14 is coated with an RGB CF layer, an organic layer and a top TC layer (as described above). With the substrate 14 stationary, the scanner 12 moves the beam over sub-areas 15 of the substrate 14 forming isolating grooves in the TC layer required to form the touch sensor electrode structure . After completion of each sub area 15, the substrate 14 is stepped to a new sub area 15 and the process repeated. This "step and scan" process is repeated until all of the substrate 14 has been patterned. Sub areas 15 can correspond to complete touch sensors for small devices (such as smart phones) or may form only part of larger touch sensors for larger devices (such as tablets and PCs). In the latter case, the sub-areas need to be 'stitched1 together to form the electrode structure of the touch sensor.

Operation of the apparatus is preferably carried out by control means, such as a computer, which is arranged to control the laser and movement of the laser to carry out the scanning processes described.

The capacitive touch sensor laser patterning process described above can be performed on substrates which each contain one or more CF devices that are subsequently aligned to and attached to LCDs or, alternatively, the laser patterning can be performed on individual devices after the CF has been aligned to and attached to the LCD.

Key aspects of the process described above are:- 1) Forming a pattern in a TC layer on top of a transparent organic layer on top of an LCD RGB colour filter 2) The pattern forms the Tx and Rx electrodes for a single layer capacitive touch sensor or forms the Rx electrodes for a two layer capacitive touch sensor 3) The TC layer is patterned to form the sensor electrode structure by direct write laser ablative scribing of narrow grooves. 4) The laser scribing process removes the TC material completely in the grooves but causes no (or minimal) damage to the underlying organic or RGB layers 5) The laser is of pulsed type emitting pulses with duration less than 80ps, and preferably less than 30ps.

Such a process differs from known processes for forming electrode structures of a touch sensor. In particular, laser scribing has significant advantages over known lithographic methods. It is much more efficient: it can be carried out more quickly, it has a much better yield than a lithographic process and it can be adapted more easily. The above process thus provides considerable advantage over known lithographic methods for forming the electrode structures of an incell touch sensor.

Claims

1. A method of forming an electrode structure for a capacitive touch sensor in a transparent conductive layer located on a transparent non-conductive layer which is located on a colour filter layer, wherein: the method comprises forming the electrode structure using a pulsed laser to apply a direct write laser scribing process to the transparent conductive layer to form grooves in the transparent conductive layer that electrically isolate areas of the transparent conductive layer on opposite sides of each groove while the transparent conductive layer is located on the transparent non-conductive layer which is located on the colour filter layer, the laser wavelength and pulse length being selected from one of the following: c. a wavelength in the range lOlOnm to 1560nm and a pulse length of 80ps or less, and d. a wavelength in the range 340nm to 355nm and a pulse length of 80ps or less.

2. A method as claimed in claim 1 in which the pulse length is 30ps or less when the wavelength is in the range 1030nm to 1064nm.

3. A method as claimed in any preceding claim in which the laser pulse length is in the range 80 to lOps.

4. A method as claimed in any preceding claim in which the laser wavelength is selected from one of the following: 1030nm, 1064nm, 1552nm.

5. A method as claimed in any of claims 1-3 in which the laser wavelength is in the range 1010 to 1070nm.

6. A method as claimed in any of claims 1-3 in which the laser wavelength is selected from one of the following: 343nm or 355nm.

7. A method as claimed in any preceding claim in which the electrode structure comprises both transmit and receive electrode structures.

8. A method as claimed in any preceding claim in which the laser beam is arranged to be scanned over a first sub-area of the transparent conducting layer, and then stepped to another sub-area and scanned thereover, this process being repeated until the required area has been scanned.

9. A method as claimed in claim 8 in which the sensor to be formed comprises a plurality of said sub-areas.