JPH1164117A - Temperature detecting method for substrate and substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form, on a print head, a temperature sensor having high accuracy in detecting the temperature of the print head. SOLUTION: This method comprises a process for forming a temperature detecting thermister on a substrate, a process for forming a plurality of thermisters adjacently to the temperature detecting thermister by the use of the same material and the same process as the temperature detecting thermister so as to have substantially the same temperature coefficient of resistance as the temperature detecting thermister, and a process for incorporating the temperature detecting thermister and one or more of the plurality of adjacent thermisters into an electrical circuit for generating a temperature-dependent output less affected by errors owing to dispersion in the temperature coefficient of resistance for reason of manufacture than in the case where one or more of the plurality of thermisters is not incorporated thereinto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink-jet printer, and more particularly, to an operating temperature of a print head using a thermistor whose resistance and resistance temperature coefficient are corrected by an auxiliary thermistor and a resistance element in order to improve temperature measurement accuracy. The present invention relates to a detection system and method.

[0002]

BACKGROUND OF THE INVENTION A known problem with thermal ink jet printers is print quality degradation due to an increase in the volume of ink ejected from print head nozzles due to print head temperature fluctuations. The size of the ejected ink droplet varies depending on the print head temperature,
As a result, print quality deteriorates. The size of the ejected ink drops varies with the printhead temperature. The reason for this is that the two properties that determine the size of the ink drop change with printhead temperature. The characteristics are the ink viscosity and the amount of ink evaporated by a firing resistor when driven by a print pulse. Printhead temperature fluctuations generally occur during printer startup, ambient temperature changes, and printer output changes.

When printing text in black and white, the print density changes with printhead temperature. This is because the density depends on the size of the ejected ink droplet. When printing grayscale images, the image contrast also changes with printhead temperature. This is because the contrast depends on the size of the ejected ink droplet. When printing color images,
The color of the printed image changes with printhead temperature. The reason for this is that the color of the print image depends on the size of all the primary color ink drops that form the color of the print image. If the print head temperature is different for each primary color nozzle, the size of the ink droplet ejected from one primary color nozzle is different from the size of the ink droplet ejected from another primary color nozzle. As a result, the color of the print image differs from the desired color. Even if all printhead nozzles are at the same temperature, if the printhead temperature increases or decreases as the page prints,
The colors are different at the beginning and end of the page. To print the highest quality text, graphics, or images, the printhead temperature must be constant.

[0004]

One of the problems associated with integrated thermistors is manufacturing variations when forming the thermistors. This variation appears as a temperature measurement error. This temperature measurement error may exceed a permissible limit near the extremes of the predetermined temperature range. This variation will be described using two examples. In the first example, the printhead temperature is monitored by a temperature sensor built on the heater substrate and made of polysilicon, which is the same material as the heater resistor. U.S. Pat. No. 4,772,866 discloses the formation of such a thermistor. The contents of this patent are incorporated herein by reference.

[0005] Polysilicon is the same material that is used in bubble-forming heaters in thermal ink jet printers. The sheet resistance of polysilicon is on the order of 40 ohms / square, and the temperature coefficient of resistance of polysilicon is 0.1 ohm / sq.
It is on the order of 001 / ° C. Since a preferred thermistor resistor (to simplify the construction of the thermistor readout circuit and increase accuracy) is typically in the range of 5,000 to 20,000 ohms, a typical polysilicon thermistor will have its length reduced to about the width. It needs to be 125 to 500 times. Such elongate thermistors are naturally placed in parallel with the array of heater elements, as described in US Pat. No. 5,075,690. With such a configuration, it responds very quickly (on the order of milliseconds) to changes in the average temperature near the heater element. Preferably, to minimize spur errors in reading by the thermistor, the two leads of the thermistor should be drawn independently of other leads on the thermal inkjet die, such as the ground line. The temperature coefficient of resistance (TCR) of a polysilicon thermistor is relatively small. This means two things: First, the signal-to-noise ratio of the polysilicon thermistor during a temperature change measurement is relatively small. Second, without having to calibrate individually,
Also, it is not practical to fabricate an accurate polysilicon thermistor without biasing the thermistor with an adjustable resistor connected in series with the thermistor. The reason is that in the process of manufacturing the polysilicon thermal inkjet heater, the manufacturing variation of the polysilicon resistance is ± 5%. When the temperature coefficient of resistance is 0.001 / ° C., the variation in manufacturing corresponds to a temperature measurement value range of ± 50 ° C. without correction. Desirable accuracy of thermistor is 1 ℃ ～ 3
Since it is on the order of ° C., some correction means must be provided. U.S. Pat. No. 5,075,690, referenced above.
By adjusting the resistance connected in series with the thermistor when the printhead temperature is at the center set point of the required temperature range, the set point temperature is then reduced to 1 ° C. It will be possible to measure with accuracy or better. As stated in the above patent,
If the normal resistance of a polysilicon thermistor is 20,000 ohms and its temperature coefficient is 0.001 / ° C, then 1 ° C
Is a resistance change of the thermistor and corresponds to 20 ohms. A ± 5% variation in polysilicon resistance corresponds to a range of ± 1000 ohms at a certain temperature. Thus, for accurate readings at the temperature set point, the resistors connected in series should have an adjustment range of 2000 ohms, for example, 3000 ohms (for devices where polysilicon exhibits the maximum value in that resistance range) to 5000 ohms. It must have an adjustment range of ohms (for devices where polysilicon exhibits the minimum value in its resistance range). Thus, the temperature measurement accuracy at the set point is as follows.

Normally, resistors are trimmed to an accuracy of 0.1%. Further, according to the specification of the thick film resistor paste, the stability of the resistor trimmed by the laser until the life thereof is reached (in a state where a load or heat is applied) is generally 0.2%.
(For example, since the TCR of the thick film resistor can be 0.00005 / ° C., the change in the resistance value is ± 0.1% with respect to the temperature change of ± 20 ° C.). Should be less than 0.3%, this total error being 5000
For an ohm trimmed resistor, this corresponds to 15 ohms. In this example, a change of 20 ohms corresponds to 1 ° C., so an error of 15 ohms corresponds to a reading error of the temperature set point of 0.75 ° C. However, U.S. Pat.
No. 5,690 does not correct for manufacturing variations in the temperature coefficient of resistance. ± 5% variation in resistance itself
Therefore, the variation of the temperature coefficient of resistance is expected not to exceed ± 10%. FIG. 1 shows that the polysilicon TCR of the measuring circuit is 0.0010 / ° C. (actually 0.000 / ° C.).
(In the range of 9 / ° C. to 0.0011 / ° C.) when the temperature is read over the temperature range of the temperature set point ± 24 ° C. Temperature set point is 36 ° C
In this case, the temperature range is from 12 ° C. to 60 ° C., which covers the temperature range required for thermal inkjet printing. FIG.
As shown in the figure, of the temperature errors at the end of the temperature range,
The portion due to manufacturing variations of the polysilicon TCR is about ± 2 ° C. Combined with the error at the set point, the total error is ± 3 ° C. This is the only margin of error that can be tolerated and may not be acceptable in some systems.

A second example of a temperature sensor formed on a thermal ink jet printhead is a drift thermistor. This drift thermistor is formed by diffusing an n-type impurity into a p-type silicon substrate on which a heater and its associated driver and logic are formed. Figure 2 shows an equivalent circuit
Shown in The ground shield is an aluminum sealing layer that stabilizes the upper surface of the thermistor. The diode in parallel with the n-type body represents a depletion layer separating the n-type body from the p-type substrate. Due to the presence of this diode, the drift thermistor must not apply a negative bias to the substrate, but can use only a positive bias.

The process for manufacturing a drift thermistor is the same as the process for manufacturing driver transistors on a Xerox printhead used in a Xerox 4004 printer. The sheet resistance is typically 5000 ohms / square,
The temperature coefficient of resistance is typically 0.005 / ° C. The optimal shape of the drift thermistor to obtain the desired thermistor resistance is a square or a rectangle with a length to width ratio of typically 0.1 to 10. When one drift thermistor is provided for each thermal inkjet die, a suitable location for installing the drift thermistor is a position corresponding to substantially the center of the heater row in the row of wire bonding pads on the back surface of the die. In this way, the thermistor measures the average temperature. In this position, the drift thermistor responds slower to the heater temperature than the polysilicon thermistor described above. From the measurement results, the response time is about 40 ms, but this response time is still fast enough to be used for on-the-fly-spot-size control. T of the drift thermistor
Since the CR is larger than the TCR of the polysilicon thermistor, its signal-to-noise ratio is excellent. However, it is still necessary to calibrate each drift thermistor or to incorporate, for example, an adjustable resistor in the external circuit. The reason is that the manufacturing tolerance of the resistance of the drift thermistor is wide, so that the fluctuation of the resistance value may be doubled. TCR can also vary widely. As a result, using the same method as before, that is, adjusting the external resistance at a given set point temperature and using the method of assuming the TCR at the center point, the temperature error in the case of the drift thermistor becomes smaller than that of the polysilicon thermistor. It can be larger than the temperature error in the case. The temperature error in this case is obtained by calculation, and FIG. 3 shows a graph thereof. In FIG.
TCR 0.003 / ° C ~ due to manufacturing variation
Although varying in the range of 0.006 / ° C, the TCR is assumed to be an intermediate 0.0045 / ° C. When an actual temperature that is significantly different from the set point temperature T ₀ where the correction resistance is adjusted by the conventional method is measured, the temperature coefficient of resistance is shifted from 0.0045 / ° C. assumed by the drift thermistor.
Temperature measurement errors become more pronounced. The error at the end of the temperature range can be ± 8 ° C., which is not an acceptable error.

[0009] These conventional temperature sensing techniques utilizing a thermistor, ie, a sensor, provided on the printhead are preferred because of their fast response to temperature changes. The most cost-effective method of manufacturing a thermistor is to manufacture the sensor as part of the substrate on which the heater resistor is formed.

[0010] A first object of the present invention is to form a temperature sensor having high detection accuracy of a print head temperature on a print head.

It is another object of the present invention to manufacture a thermistor on a printhead substrate by correcting for manufacturing variations in establishing the temperature coefficient of resistance of the thermistor.

[0012]

The above and other objects of the present invention are also provided.
Another object is achieved by manufacturing a thermistor having a novel correction circuit that minimizes all possible errors, including manufacturing TCR variations with respect to printhead temperature sensing. This correction circuit is manufactured near the main thermistor. The correction circuit may comprise one or more auxiliary thermistors of the same type as the main thermistor but with a small resistance value, and may be used in combination with externally adjusted resistors to further reduce temperature errors.

More specifically, the present invention relates to a method of detecting the temperature of a silicon substrate, and in accordance with one aspect of the invention, forming a temperature detecting thermistor on the substrate, and having a resistance temperature coefficient substantially equal to the temperature detecting thermistor. Forming a plurality of thermistors adjacent to the temperature detection thermistor with the same material and process as the temperature detection thermistor, and one or more of the temperature detection thermistor and the plurality of adjacent thermistors, Incorporating a temperature-dependent output that is less susceptible to errors due to manufacturing variations in temperature coefficient of resistance than if one or more of the plurality of thermistors were not incorporated. .

According to a second aspect of the present invention, there is provided a method for detecting a temperature of a substrate, comprising forming one side of a bridge circuit,
Forming a temperature detecting thermistor having a resistance value represented by R ₁ = R _t = r ₀ (1 + aΔT) on a substrate (where a represents a temperature coefficient of resistance (TCR) and r ₀ represents a set point temperature T ₀ represents the resistance at ₀ , ΔT represents the difference between the measured temperature and the set point temperature T ₀ ), and a plurality of partial thermistors having a TC equal to the TCR of the temperature sensing thermistor.
R, and the partial thermistor is adjacent to the temperature sensing thermistor such that the combined resistance of the partial thermistor is fR ₁ (where f = 1−B / a, and B represents a preselected minimum TCR value). Forming, and incorporating the partial thermistor and the external resistance R _x = r ₀ (1-f) into a bridge side adjacent to the R ₁ side including the temperature detection thermistor.

[0015] According to this aspect of the present invention, there is provided a substrate, disposed in said substrate, TCR resistance at R _t
And a temperature detection thermistor of a, disposed adjacent to the thermistor, the same material as the temperature detection thermistor,
And a partial thermistor made simultaneously therewith in the same manner as used for the temperature sensing thermistor, with a TCR of a and a nominal resistance of fR _t (where f is less than 1).

Hereinafter, the present invention will be described from the viewpoint of improving the temperature detection accuracy of the drift thermistor. Because,
As described above, this type of sensor has a maximum error at the end of the required temperature range. However, the invention can be applied to other types of thermistors formed on or within a printhead substrate, and more generally, to correct for variations in the thermistors in applications other than the printhead.

Prior Art Document US Pat. No. 5,075,69
In No. 0, a voltage having a magnitude depending on the output of the thermistor was generated using a bridge circuit as shown in FIG. Referring to FIG. 4, the bridge circuit 10 has resistances on four sides (R _{1 to} R ₄ , and a sensor thermistor is included in the side R ₁ ).
have. External voltage V _in is applied from a voltage source 12, bridge voltage V _out is dependent on the relationship between the resistance value of each side, for example, changes in response to changes in the resistance of one or more sides. The general bridge equation for V _out is as follows:

[0018]

(Equation 1)

Arranging as R ₂ = R ₄ ,

[0020]

(Equation 2)

## EQU1 ##

US Pat. No. 5,075,690, referenced above.
In the above prior art, at a certain set temperature T ₀ , R ₁ was set equal to R ₃ by adjusting a resistor provided in series with the thermistor at R ₁ . To simplify the description of the prior art, R ₁ = r ₀ (1 + aΔ)
T). Here, R ₁ = R _t is _satisfied when the resistance at T ₀ is r
₀ , a thermistor with TCR = a. ΔT = T−
T ₀ . In the prior art, when T = T ₀ , R ₃ = r ₀
Adjust to In this conventional example, from equation 2,

[0023]

(Equation 3)

Therefore,

[0025]

(Equation 4)

In the case of the prior art, a certain TCR = A is assumed because there is a variation in TCR in manufacturing. When calculating the error ΔT for FIGS. 1 and 3, the actual TCR =
_Vout was calculated by Equation 3 using a. Further, ΔT was calculated by Equation 4 using the assumed TCR = A (here, A = 0.001 / ° C. in FIG. 1, A A in FIG. 3).
= 0.0045 / ° C).

[0027] In the present invention, not only adjustable external resistor, made of the same material as the sensor thermistor R _t, minimize measurement errors by incorporating also a series of thermistors disposed in proximity to R _t to the side R ₃ As much as possible. By shorting the various combinations of these "parts" thermistor has the same resistance coefficient R _t, fR _t (where the f to accommodate the full range of production tolerance of the thermistor TCR usually 1 the resistance value so as to have a nominal value of a is) less than can be provided in R ₃ sides. Figure 5 shows a bridge circuit which is a modification of the R ₃ sides. FIG. 6 shows one way of implementing the proposed thermistor configuration on a chip.

Referring to FIG. Thermistor R
_t is connected in series with some other thermistor of the same material as R _t but with a resistance that is partial with respect to R _t . The length of the thermistor R _t is twice the width (eg, 200 microns × 100 microns). The width of each partial thermistor is the same, but the length is continuously reduced, and the length of the shortest thermistor (R _t / 16) is, for example, 12.5 microns. All thermistors are shaded. White pads represent wire bonding pads, usually aluminum. Thermistor sensor R _t is placed between the pads P ₁ and P ₂ in R ₁ side of the bridge. Therefore, R ₁ = R _t = R ₀ (1 + aΔ)
T). Here, R ₀ is the resistance value a + T ₀ , Δt = T
−T ₀ . In R ₃ sides, partial resistance of the selected combination located between the pad P ₂ and P ₃ are arranged in series with an adjustable external resistor R _x. Arranged in parallel with each partial resistor is a fusible link short bar 30. Soluble link electrically melted or cut by laser, it is possible to obtain partial thermistor resistance any combination, R _t / 1 from 0 to 15R _t / 16
Set in increments of 6. Also, R ₃ = R _x + fr
₀ (1 + aΔT). Here, since the partial thermistor is close to R _t , the TCR = a of the partial thermistor is essentially the same as the TCR of R _t .

The output voltage of the bridge is obtained by substituting the values of R ₁ and R ₃ into Equation 2.

[0030]

(Equation 5)

When R _x is adjusted to the value of r ₀ (1-f),
Equation 5 is simplified as follows.

[0032]

(Equation 6)

To summarize this,

[0034]

(Equation 7)

## EQU1 ##

In general, even at the end of the temperature range, V
_out is less than 4% of V _in. Therefore, Equation 7 can be approximated as follows (the most accurate when f = 0):

[0037]

(Equation 8)

When f = 1-B / a

[0039]

(Equation 9)

## EQU4 ##

Determine which fusible links to cut,
The algorithm for determining how much the value of the external resistor should be set to minimize the measurement error of ΔT = T−T ₀ is as follows. Let B be the minimum value of TCR that can be tolerated as manufacturing variations. Measuring the actual TCR = a for thermistor R _t of a printhead die. Then, the total resistance of the combination of partial thermistor which is not short-circuited in the edge R ₃ is such that fR _t, cleaves soluble links on the printhead die. Here, f is substantially equal to 1-B / a. Finally, to adjust the external resistor R _x such that _{R x = r 0 (1-} f). Here, r ₀ is the value of R _t at T = T ₀ .

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In an embodiment for minimizing an error when measuring .DELTA.T in Equation 9, several conditions are first assumed. Determine the minimum value of TCR that can be tolerated as manufacturing variations. As shown in FIG. 3, for a drift thermistor, the minimum TCR = B for R _t is 0.003 / ° C. For a particular thermistor R _t formed to a printhead on the die, the actual TCR
Is measured. (Suitable to make this measurement during a wafer probe test, measure all thermistors on the wafer at room temperature, then re-measure all thermistors when the wafer is held on a hot stage.)
TC for a specific die in an embodiment of the present invention
Assume that the actual measured value of R is 0.004 / ° C.

When f is obtained from Expression 9, f = 1- (0.0
03 / 0.004) = 0.25. Next, bar 30
Melts the fusible link connected to R _t / 4 and shorts this resistor. Accordingly, the resistance value of the partial resistance which is not short-circuited in the edge R ₃ becomes fR _t = 0.25R _t. Then, to satisfy the formula _{R x = r 0 (1-} f) = 0.75r 0, to adjust the external resistor R _x. Where r ₀
Is the value of R _t at T ₀ .

As shown in FIG. 7, the temperature measurement error in the case of the drift thermistor is greatly reduced as compared with the case of the prior art shown in FIG. 7 having the same manufacturing variation of TCR = a as in FIG. 3 is also used in FIG. Since the maximum value of TCR (0.006 / ° C.) is more than twice the minimum value of TCR (0.003 / ° C.), the R _t / 2 partial thermistor and R _t / 4, R _t / 8, R _t / 16 The configuration shown in FIG. 6 including each of the partial thermistors is used. In the calculation of the ΔT measurement error when the configuration of FIG. 6 is used, the actual TCR value (= a) for each case is used to calculate V
calculated _out . Here, the set value of f is shown in FIG.
F = 1−B / a given in 1/16 unit by the configuration of
Is set to the value closest to the calculated value of f. B was set to the assumed minimum value of a (0.003 / ° C.). Next, ΔT was calculated for each assumed value of ΔT using Equation 9, and the difference between the assumed value and the calculated value was displayed as a temperature error in FIG. It should be noted here that in using Equation 9, it is not necessary to know the value of f used in the print head. Therefore, this algorithm is
All adjustments of the partial thermistor and external resistance are performed at the factory, and no special measurements or adjustments need to be made for different printheads for each user or for each printer. As can be seen from FIG. 7, the present invention significantly reduces the temperature measurement error. The maximum measurement error occurs when ΔT is the end point of the range (for example, ± 24 ° C. in the embodiment of the present invention), and when the TCR is away from its minimum value B (that is, when the value of TCR is big,
Therefore, the case where the value of f is large) and the case where the available discrete value of f (because it increases in 1/16 unit) do not fit well with the calculated value of f. Therefore, in FIG.
The maximum error of the measured value of T (−2.3 ° C.) is TCR = a =
In the case of 0.0055 / ° C., it occurs when the assumed value of ΔT is −24 ° C. TCR is larger when TCR = a = 0.006 / ° C., but the calculated value 0.5 of f is 1/1 in FIG.
F = 0 to f = 15/16 provided in a 6-unit configuration
Exactly equal to one of the discrete values in the range. TCR = a =
In the case of 0.0055 / ° C., the calculated value of f is 0.455, and the closest discrete value of f in the above range is 0.43.
8 For an extreme value of + 24 ° C., the maximum error of ΔT is T
Occurs when CR = a = 0.006 / ° C and its value is-
It will be 1.6 ° C.

The calculation result of FIG. 7 does not include an adjustment error of the external resistance _Rx . As mentioned earlier, laser trimming is usually performed with an accuracy of 0.1%, and the stability (including temperature excursions) of the laser trimmed resistor is 0.1%.
2% is expected. Therefore, it is necessary to consider the error 0.3% of _Rx . Since the temperature error in FIG. 7 is larger on the negative side (the maximum negative error is -2.3 ° C. and the maximum positive error is 0.2 ° C.), _Rx is its target value r ₀ (1−1).
Consider a case 0.3% larger than f). As shown in FIG. 8, due to this resistance adjustment error, the measured temperature curve in FIG. 7 moves in the negative direction. Even so, FIG.
Is −2.8 ° C., and TCR = a
It occurs at -24 ° C when = 0.0055 / ° C. The maximum error at the other end of this temperature range is -2.1
° C, and +24 when TCR = a = 0.006 / ° C.
It occurs at ° C. Therefore, the temperature measurement accuracy was improved as compared with the case of FIG. 3 in which an error of ± 8 ° C. (range of 16 ° C.) could occur. Specifically, in the method of the present invention, even when the trimming error is considered, the maximum temperature error is less than 3 ° C., and the error range is also less than 3 ° C. If it is possible to make the manufacturing variation range of the TCR smaller than twice the difference between the maximum value and the minimum value of the TCR, it is necessary to improve the accuracy of the present invention and to increase the part of R _t / 2. This is convenient because there is a possibility that the thermistor can be deleted. However, even if the manufacturing variation is twice the above difference, the temperature measurement accuracy can be maintained at 3 ° C. over the temperature range and the entire print head.

[0046] V _out in FIG. 5, changes in response to changes in the resistance value of the thermistor R _t due to temperature changes of the printhead. As known in the art, V
_out can be amplified and converted to a digital signal.
This digital signal is sent to a control circuit of a system control device which monitors and corrects the temperature change, for example, changes the pulse of the drive signal sent to each resistor.

Various modifications of the above embodiment are conceivable. For example, although the incorporation of an external resistor R _x on the print head which is most likely form in the external resistor desirable r ₀ (1-f) values using any of the methods are several in this case Can be set. When an electrical connection board for a printhead is made using thick-film (or thin-film) technology, the external resistors are screen printed and baked (or deposited and molded) as part of the substrate. afterwards,
Laser trimming is performed so that the thermistor and the TCR of the connected thermal inkjet die have a specific value. When the electrical connection board is made by printed wiring board technology, the external resistance is mounted on the electrical connection board as a separate component adjustable by laser. Or,
When mounting the printhead, one or more individual resistors may be selected from a variety of resistors for which the total resistance is an appropriate value. There are various methods for detecting the value of f used. If the fusible link is melted during the wafer test phase, then R
at the time of setting the value of _x, the ratio of the thermistor resistance between the thermistor resistance and the pads P ₁ and P ₂ between the pad P ₂ and P ₃ is f (see FIG. 6). Alternatively, all of the pads of FIG. 6 can be pulled out to the printhead board and a fusible link that has not melted can be detected as a short circuit. In fact, a short bar for the partial thermistor can be provided on the electrical connection plate of the printhead, and the value of f can be set during printhead mounting rather than during wafer testing.

Various other configurations of the selectable partial thermistor are possible. In the configuration of FIG.
The thermistors are in series with each other and each thermistor is provided with a fusible link in parallel. However, it is also possible to install the thermistors in parallel with each other and to install the fusible link in series with each thermistor. The resistance value of the partial thermistor is sequentially set so as to be half the resistance value of the partial thermistor located immediately before. This configuration has the advantage that the accuracy of f can be maintained over a wide range using relatively few elements. However, other configurations are of course possible.

As another modification, the value of TCR is the temperature T ₀
If it correlates well with the r ₀ value of the thermistor at
To determine the TCR, it is not necessary to measure the thermistor at two different temperatures, but only at T ₀ and use this correlation to predict the TCR. This approach may not be accurate enough when comparing the full range of wafers, but may be useful, for example, when applied within a wafer of a manufacturing unit (batch).

To increase the bridge output voltage per 1 ° C. of temperature change, a relatively large value of the input voltage can be used. In general, the V _in the order of 10 volts. The upper limit is set by the heat generated by the thermistor itself. Alternatively, V _out can be amplified to increase sensitivity.

The method of the present invention, which corrects for not only manufacturing variations in the value of the thermistor at a particular temperature, but also manufacturing variations over the TCR range, eliminates the need for active components on the printhead. Only a passive network need be provided. Therefore, this method is compatible with the currently used printhead manufacturing technology. More generally, the idea of using a combination of close-range thermistors that can be selected in combination with an adjustable external resistor means that the thermistor values and TCR manufacturing variations are too large to provide sufficient temperature measurement accuracy. The present invention can be applied to any element (element other than on the thermal ink jet print head) that cannot obtain the above, and is not limited to only the thermal ink jet print head.

[Brief description of the drawings]

FIG. 1 shows a temperature coefficient of resistance (TC) of a polysilicon thermistor.
9 is a graph showing a temperature measurement error range caused by manufacturing variation of R).

FIG. 2 is an equivalent circuit diagram of a drift thermistor formed on a p-type silicon substrate.

FIG. 3 is a graph showing a temperature measurement error range caused by manufacturing variations of the TCR of the drift thermistor.

FIG. 4 is a schematic electrical circuit diagram of a conventional bridge circuit used to generate a voltage that changes in response to a change in the resistance of any one side.

FIG. 5 is a schematic electrical diagram of the bridge circuit of FIG. 4 modified according to the present invention by manufacturing to include a partial resistance on one resistance side.

FIG. 6 is a portion of a printhead substrate manufactured to include a thermistor connected to a fractionally adjusted resistor.

FIG. 7 is a graph showing a temperature measurement error range caused by manufacturing variations of a TCR of a drift thermistor forming a part of the circuit of FIG. 5;

FIG. 8 is a graph of FIG. 7 corrected in consideration of an influence of a laser trimming error.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Joseph J. Wissock United States 14580 New York Webster Crest Circle 544 (72) Inventor Thomas P. Courtney United States of America 14450 Fairport Ross Common Crescent, New York 48 (72) Inventor Juan Jay. Bethela USA 14580 New York Webster Clarendon Court 453 (72) Inventor Thomas E. Watlowski, USA 14526 Penfield, New York Atlantic Ave 3531 (72) Inventor Joseph F. Stephanie United States 14589 Williamson Lake Road, New York 3369 (72) Inventor Richard Buoy. Radonna United States 14450 New York Fairport Grandview Drive 67

Claims (3)

[Claims] 1. A method for detecting a temperature of a substrate, comprising: forming a temperature detection thermistor on a substrate; and using the same material and process as the temperature detection thermistor so as to have substantially the same temperature coefficient of resistance as the temperature detection thermistor. Forming a plurality of thermistors adjacent to the temperature detection thermistor, and not incorporating one or more of the temperature detection thermistor and the plurality of adjacent thermistors, one or more of the plurality of thermistors Assembling into an electric circuit that generates a temperature-dependent output that is less susceptible to errors due to manufacturing variations in resistance temperature coefficient than in the case. 2. A method for detecting a temperature of a substrate, comprising forming one side of a bridge circuit, wherein R ₁ = R _t = r ₀ (1+
a) forming a temperature detecting thermistor having a resistance value represented by a ΔT on a substrate (where a represents a temperature coefficient of resistance (TCR), r ₀ represents a resistance at a set point temperature T ₀ , and ΔT represents a measurement temperature and represents the difference between the set point temperature T ₀₎ for a plurality of partial thermistors (fractional thermistor), has a substantially equal TCR and TCR of the temperature detection thermistor, and a combination resistance of the portion thermistor fR ₁
(Where f = 1-B / a, where B represents a preselected minimum TCR value), forming adjacent to the temperature sensing thermistor; and the partial thermistor and external resistance R _x = r ₀ temperature detection method of a substrate comprising the steps of incorporating the bridge sides adjacent to R ₁ side containing (1-f) said temperature sensing thermistor. 3. A substrate is disposed in the substrate, a temperature detecting thermistor TCR resistance at R _t is a, is disposed adjacent to the thermistor of the same material as the temperature detecting thermistor Wherein the TCR is a and the partial thermistor has a nominal resistance of fR _t (where f is less than 1), simultaneously made in the same manner as used for the temperature sensing thermistor.