JPS6117124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method of manufacturing graphic tablets as described in U.S. Pat. No. 4,087,625. The tablet is particularly adapted to be mounted on a display surface (such as a gas panel or CRT). After all, this is the X and Y position of the pen held on the surface of the display.
This is because only a single layer of thin transparent metal electrodes is required to sense the coordinates, as opposed to a structure where there are two layers of orthogonal electrodes (and an intervening insulating layer). This single metal layer is shaped to provide a rectangular resistive voltage divider across the top and bottom (or sides) of the active area of the tablet. Complementary shaped triangular electrodes extend along only one direction from the two voltage dividers. These triangular electrodes are supplied with an alternating voltage which is capacitively coupled to a pen held at a point selected by the user on the display. Pen voltage is proportional to the pen's position in the tablet's X-Y coordinate system.

To establish a linear relationship between the pen position along the X direction and the amplitude of the pen signal, the two voltage divider resistors need to be infinitely linear (in the Y direction, the linearity of the resistors is less important for operation). This linearity is achieved by forming the rectangular resistors and triangular electrodes on a glass substrate by any technique suitable for economical large-scale manufacturing and individually trimming the resistors. It is a general object of the present invention to provide a new and improved method and apparatus for trimming such resistors.

Description of the Prior Art The prior art has proposed many techniques for trimming thin film resistors. Certain features of these techniques are incorporated into the preferred method of the invention described below. Although other features of the prior art are unsatisfactory to the present invention, a brief description of the prior art will provide a suitable introduction to the objects and features of the present invention.

U.S. Pat. No. 4,184,062 discloses a resistor formed from a piece of thin film material in which trimming cuts are made along one side of the resistor by a laser. As the laser trim operation progresses from one end of the resistor to the other, the resistance of the trim operation point to ground is measured. The precision master resistor slider is moved in steps with the trimming operation. If the resistor being trimmed is accurate, the voltage on the master resistor slider is equal to the voltage at the trim point. The circuit senses any difference between two voltages,
The cutting motion is moved inward and outward as necessary to increase or decrease the resistance of the resistor being trimmed. In comparison with this reference, it is an object of the present invention to provide a method and apparatus for trimming a resistor without using ohmic contact probes on the surface of the resistor. Another related object of the invention is to linearly trim a resistor regardless of the absolute value of the resistance. A related object of the present invention is to remove a minimum amount of conductive layer to linearly trim the resistor to provide linearity and maintain a minimum resistance value. It is an object of the present invention to provide a simple new resistor trimming method that can be used to perform a second trim to increase linearity, at least to an initially trimmed resistor.

In other techniques, small notches are formed along the sides of the resistor to increase the resistance. This technique is accurate only if the measurement and trim are taken together. One of the objects of the present invention is to provide an improved method of resistor trimming in which the measurements of the resistor are made independent of the trimming operation. An advantage of the present invention is that alignment of the display surface and the tablet can be achieved with minimal misalignment.

In the method of the present invention, the resistance of the tablet resistor is first measured at discrete points using a capacitive voltage probe similar to a pen used in normal tablet operation. When a resistor is formed into a thin film using ordinary resistance materials, pinholes are likely to exist in the thin film, so even if they do exist, the pinholes will not affect the resistance reading. A capacitive probe is used so that measurements can be made over a sufficiently large area. The resistance measurements are stored in a data processing system to create a resistance profile for resistor trim operations. The trimming operation is accomplished by conventional equipment such as an electroetcher. Resistance is measured again and a second or subsequent trim is performed if necessary.

Parts of the tablet that are particularly relevant to the method of the invention will be described below. The tablet is shown in FIG. 1 in a vertical plane when used with a display device, or in a horizontal plane as when used in applications such as providing handwritten input to a computer system. It can be thought that it exists inside. top, bottom, sides,
The terms upper, lower, right, and left are used to designate position and orientation within the plane of the drawing. Movements perpendicular to the plane of the drawing are called "up" and "down", as is commonly done to describe the position of a hand-held pen.

The tablet has a glass substrate 12. A thin film of a transparent conductor, such as indium-tin oxide, is deposited on the surface of the glass and then etched to form a pattern of electrodes shown as 14-29. Triangular electrodes 18, 19 form the tablet area and these electrodes are energized to establish a voltage that can be sensed capacitively by a conventional capacitive pen (not shown). Pen voltage is proportional to pen position in either the X or Y direction, depending on how the electrodes are energized. Screen printed wide metal tabs 26-29 connect the electrodes to a circuit for normal operation to establish an alternating current voltage gradient across one direction of the tablet. These tabs are also used to apply test voltages to the electrodes for the manufacturing steps of the invention. Triangular electrodes 18, 19 are arranged in pairs. Each triangular electrode has a rectangular area 14, 15 forming a voltage dividing resistor by connecting electrodes 16 and 17.
It is connected to the.

In the embodiment of FIG. 1, the triangular electrodes 18, 19 extend vertically and the resistors 14, 15 are located horizontally along the top and bottom sides. This is because the entire area of the tablet is normally rectangular in shape, wider than it is high, and this electrode orientation makes the area occupied by the resistor smaller. Therefore, from a more general point of view, resistors are present along two opposite sides of the tablet.

In a subsequent stage of the manufacturing process, an additional transparent layer is formed over the layer of metal electrodes. These layers slightly separate the pen from the triangular metal electrodes and average out the effect of discrete nearby electrodes on the voltage sensed by the pen. As a result, the pen connects 16,
The discrete voltage steps established by 17 are sensed. The normal operation of the tablet will now be reviewed as an introduction to the related resistance measurement operations described below.

To sense the pen position in the Y direction, the upper resistor 14 (or lower resistor 15) is connected by grounding its two tabs so that each of the associated triangular electrodes 18 is also at ground potential. and is held at ground potential all along its length. The lower resistor 15 (or upper resistor 14) is connected across its length by connecting both tabs to the AC voltage terminals so that each of the associated triangular capacitor elements 19 receives this AC voltage. A uniform alternating voltage is considered. When the pen is positioned on the tablet, it receives an alternating voltage by capacitive coupling to the nearby triangular electrodes 18,19. This capacitive coupling is directly proportional to the area of the pen's field of view. When the pen is positioned below the tablet, it receives almost the full AC voltage of resistor 15. As the pen is moved towards the top of the tablet, the capacitive coupling to electrode 19 (which is at ground potential) increases and the voltage on the pen drops in proportion to its Y position.

When the tablet operates in the mode described above,
Horizontal movement of the pen across the tablet without changing its position in the Y direction should not result in a change in the pen voltage. To configure the linearity of this tablet, the voltage at each connecting electrode 17 (or 16) is connected to the triangular electrodes 18 and 19.
The capacitive charging current flows through the resistors 14 and 15 and must remain substantially the same despite the fact that the force is greater towards the outer ends than towards the center of the resistors. Therefore, for accurate Y-direction operation, resistors 14 and 15 must have low resistance values. Resistor 14,1
The thickness of 5 must be limited by the requirement that the associated triangular electrodes 18, 19 must be thin in order to be transparent. resistor 14,
The width of 15 is limited by the requirement to form as large an effective area of the tablet as possible within the limited overall dimensions of glass substrate 12. Therefore, it is an object of the present invention to provide a resistor trim operation that holds each individual tablet at the lowest possible resistance (rather than trimming each tablet's resistor to a specific resistance value).

To sense the position of the pen in the X direction, the left (or right) end of each resistor 14, 15 is held at ground potential and the right end is provided with the same AC voltage as described above. The two resistors 14 and 15 are connected to the electrode 1 to which the potential of the connection electrode of the triangular electrode 18 corresponds.
The connection electrodes 17 of No. 9 are formed linearly so as to have the same potential. The pair of triangular electrodes 18, 19 thus has the effect of a single rectangular electrode on the potential of the associated connection element 16, 17. When a linear tablet operates to sense the position of the pen in the X direction, the pen moves up and down the tablet at a constant X position without changing the voltage sensed by the pen. obtain. When the pen is moved left and right across the tablet,
The pen voltage increases uniformly (or decreases if the connections are reversed). For this operation each resistor 14, 15 must be linear so that the alternating voltage is the same at corresponding points on the two resistors. However, the total resistance values of the two resistors need not be the same.

Measurement of linearity of a resistor - FIG. 2 FIG. 2 is a side view of the glass substrate 12 and the sides of the resistor 15 (or 14). The resistance measuring probe 34 has a metal electrode 35 and a suitably insulating body 3.
It has 6. Body 36 is preferably any plastic having a high dielectric constant to increase capacitive coupling. Electrode 35 has an appropriate spacing from tablet electrode 15. Tablet electrode 1
5 (or 14) and probe electrode 35 and intervening insulator 36 form a capacitive circuit such that the probe voltage is related to the voltage at the tablet electrode as in normal tablet operation using a pen.

A tablet structure consisting of substrate 12 and electrodes is positioned in a vacuum test fixture or other suitable fixture (not shown) and probe 34
are connected by an X-Y positioning mechanism by conventional means as represented by line 38. The probe is first positioned at one end along the approximate centerline of resistor 14 or 15 (avoiding edge effects) and then stepped in approximately 1.27 cm increments along the resistor. During this resistance test, the oscillator 40
supplies AC voltage to the tab located at the right (or left) end. The other end of the resistor is connected to ground. Therefore, the voltage of oscillator 40 is tab 2
9 and 27, resistor 15 divides this voltage by its resistance, and an alternating voltage gradient appears along the length of the resistor. This alternating voltage is linear with respect to the length of the resistor according to the uniformity of the resistance value.
The voltage in the area of the resistor 15 below the probe electrode 35 is capacitively supplied to the electrode and this voltage is transmitted to the other elements of the system. A conventional analog-to-digital converter 44 and a conventional data processor 4
5 stores the probe voltage and incremental value.

This capacitive measurement technique avoids some of the problems that can occur with ohmic contact probes. For example, the spacing between electrodes 15 and 35 produces an averaging effect as described for tablet operation. This spacing is the resistor 14, 15
(the probe electrode contacts an appropriately sized area of the electrode) to average out the effects of pin holes that may occur therein. Alternatively, the spacing between electrodes 35 and 14 or 15 can be made small to provide good capacitive coupling for strong signals and to avoid effects from any nearby sides of the resistor.

Resistance Value Data FIGS. 3, 4, and 5 FIG. 3 is a graph illustrating how to use the above-mentioned resistance value measuring device. Numbers 0 through 10 along the horizontal axis represent discrete sample points. The vertical axis represents the measured voltage, or equivalently the resistance up to the ground tab. The lines connecting points on the graph are slightly nonlinear. This nonlinearity can be solved by calculating the least mean square error linear function (normal statistical function) by linear regression analysis,
It is measured by comparing the actual voltage or resistance value to this linear function. If these points are within a suitable percentage (preferably 0.25%), the resistor is acceptable for production without trimming.

Figure 4 is similar to Figure 3 except that the left vertical axis represents the incremental resistance or difference between the sample point identified on the horizontal axis and the previous (or next) sample point. . In other words, the height of the point in FIG. 4 corresponds to the slope of the line in FIG. FIG. 4 likewise has a right vertical axis on which the resistance values are normalized by dividing each value by the highest value occurring at points 5 and 6. Points 5 and 6 thus have a normalized value of 1, and the other points have smaller normalized values. This normalized value indicates the absolute width that will be trimmed as explained below.

FIG. 5 is a mirror image of FIG. 4 and is formed by subtracting the normalized value in FIG. 4 from 1. Points 5 and 6 therefore have the largest incremental value of resistance of 1.
has a zero value in the function of FIG.

It is known that the function shown in FIG. 5 is an appropriate resistance value change characteristic for the resistor trim operation. This may be intuitively obvious from the fact that no trim is required at points 5 and 6 of the highest incremental resistance values. Similarly, the maximum trim must be made at point 2 where the minimum incremental resistance is measured.

Trim Operation - Figures 6 and 7 Trimming cuts are preferably performed by a spark etch machine as shown in Figure 6;
Similar metal cutting operations are also performed with lasers. However, the present invention is applicable to a variety of metal cutting techniques. The data processing device 45 is
Appropriate commands are provided to the step mechanism 39 to position the electrode 50 of a conventional spark engraver along the desired path. The metal foil 15 is connected in circuit with a current source 51 for the spark etching device. 6th
The illustrated apparatus typically illustrates one technique for forming trim cuts.

FIG. 6 shows a resistor 15 with a cut 53 creating a selvage 15'. The trimming resistance value change characteristic shown in FIG. 5 is tracked stepwise by the X-Y mechanism 39. Therefore, the actual trim approximates a continuous function of resistance value in relation to position on the resistor. The cutting device preferably moves along the length of the resistor (X direction) by 0.254 cm or 1/5 of the distance between the sample points. After one increment of movement, device 39 steps up or down in the Y direction, such as around sample point 2, or continues, such as between points 7 and 8.

The width of the step in the Y direction is found from the normalization operation as shown in FIG. In the exaggerated example for illustration purposes, the incremental resistance value at point 8 is a fraction of the maximum value occurring at points 5, 6, and 10.
It is 2/3. Since the incremental resistance value is (approximately) proportional to the width of the resistor, reducing the width at point 8 to 2/3 of the total width increases the incremental resistance value to the value at the maximum point.

After the resistor is trimmed, the resistance measurements of FIGS. 2 and 3 are repeated. In many cases, a single trim operation brings the resistance value to the desired linearity. If not, a second trim operation is performed. This operation is similar to the steps previously described except that the width of the second trim is calculated from the line 53 of the first trim.

Other Embodiments The present invention is also useful in other applications where metal thin film resistors are trimmed to be linear, but the actual resistor value is within a specified range. Capacitive probes and associated alternating voltage circuits are known to be particularly useful with metal thin film resistors, but the probes avoid problems caused by pin holes when only contact probes are used. Therefore, the invention is also suitable for applications where the thin film is electrically insulating or cannot be connected by ohmic probes. The invention may be implemented with a variety of mechanical step devices and a variety of metal cutting techniques. Statistical and algebraic techniques for calculating trimmed resistance change characteristics from resistance samples are well known and can be easily implemented in many programming languages. Although the analysis of resistance measurement techniques has been described in terms of resistance values, this can also be equivalently expressed in terms of conductivity (reciprocal of resistance) or other terms.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a tablet according to the method of the invention. FIG. 2 is a side view of a tablet and an apparatus for measuring resistance change characteristics in one step of the method according to the invention. FIG. 3 is a graph of the resistance measurement stage. FIG. 4 is a graph showing the calculation of resistance value change characteristics for resistor trimming. FIG. 5 is a top view of the resistor of the tablet of FIG. 1 showing a trim operation. FIG. 6 is a diagram similar to FIG. 2 showing the resistor trim operation and apparatus. FIG. 7 is a diagram illustrating a resistor and trim operation similar to FIGS. 3-5. 12... Glass substrate, 14, 15... Rectangular area forming a voltage dividing resistor, 16, 17... Connection electrode, 18, 19... Triangular electrode (active area of tablet), 26, 27, 28, 29...Tab for circuit connection.

Claims (1)

[Claims] 1. Apply an alternating voltage across a resistor, measure the voltage across the resistor, store a resistance measurement value according to the measured voltage, and calculate a resistance value from the measurement value. In the resistor trimming method of trimming the resistor according to the method, when the resistor is a metal thin film resistor, the voltage measurement measures a voltage change along the length direction of the metal thin film resistor. 1. A method for trimming a metal thin film resistor, comprising using a voltage probe that moves relatively along the length of the resistor to capacitively couple the resistor.