Abstract:
In manufacturing or adjusting an electron-emitting device which has at least two electrodes and emits electrons by applying a voltage between the two electrodes, or before performing normal driving, a voltage V 1  is applied which has the following relationship with a maximum voltage value V 2  applied as a normal driving voltage to the electron-emitting device between the two electrodes. Giving a current I flowing upon application of a voltage V when the voltage V falling within a voltage range causing electron emission upon application of the voltage between the two electrodes is applied between the two electrodes: 
     
       
           I=f ( V ) 
       
     
     and letting f′(V) be the differential coefficient of f(V) at the voltage V, the voltage V 1  has a relationship with the voltage V 2  that satisfies, upon application of the voltage, the first condition: 
     
       
           f ( V   1 ) /{V   1   ·f′ ( V   1 )− 2   f ( V   1 ) }&gt;f ( V   2 ) /{V   2   ·f′ ( V   2 )− 2   f ( V   2 )} 
       
     
     Further, letting Xn- 1  be the value of the right side of inequality (2) upon a first application of the pulse-like voltage V 2  when the voltage V 2  is applied as pulses successively twice between the two electrodes after application of the voltage V 1 , and Xn be the value of the right side of inequality (2) upon a second application of the pulse-like voltage V 2 , the relationship with the voltage V 2  satisfies the second condition that Xn −1  and Xn satisfy: 
     
       
         ( Xn - 1   −Xn ) /Xn - 1 ≦0.02

Description:
FIELD OF THE INVENTION 
     The present invention relates to an electron-emitting device manufacturing method and apparatus, driving method, and adjusting method thereof. 
     BACKGROUND OF THE INVENTION 
     Conventionally, electron-emitting devices are mainly classified into two types of devices: thermionic and cold cathode electron-emitting devices. Known examples of the cold cathode electron-emitting devices are field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter), and surface-conduction type of electron-emitting devices (to be referred to as SCE type electron-emitting devices hereinafter. 
     Known examples of the FE type electron-emitting devices are disclosed in W. P. Dyke and W. W. Dolan, “Field emission”, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, “PHYSICAL Properties of thin-film field emission cathodes with molybdenum cones”, J. Appl. Phys., 47, 5248 (1976). 
     A known example of the MIM type electron-emitting devices is disclosed in C. A. Mead, “Operation of Tunnel-Emission Devices”, J. Appl. Phys., 32,646 (1961). 
     A known example of the SCE type electron-emitting devices is disclosed in, e.g., M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965). 
     The SCE type device utilizes the phenomenon that electrons are emitted from a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The SCE type electron-emitting device includes electron-emitting devices using an SnO 2  thin film according to Elinson mentioned above [M. I. Elinson, Radio Eng. Electron Phys., 10, 1290, (1965)], an Au thin film [G. Dittmer, “Thin Solid Films”, 9,317 (1972)], an In 2 O 3 /SnO 2  thin film [M. Hartwell and C. G. Fonstad, “IEEE Trans. ED Conf.”, 519 (1975)], a carbon thin film [Hisashi Araki et al., “Vacuum”, Vol. 26, No. 1, p. 22 (1983)], and the like. 
     The FE, MIM, and SCE type electron-emitting devices have an advantage that many devices can be arranged on a substrate. Various image display apparatuses using these devices have been proposed. 
     It is known that characteristic changes in actual driving can be suppressed by applying a voltage higher than a voltage applied in the actual driving in the manufacturing process of the SCE type electron-emitting device. 
     An image display apparatus formed using the electron-emitting devices must maintain brightness and contrast suitable for image display over a long term. 
     To realize this, the electron-emitting device must emit a predetermined electron amount or more in an expected term, while suppressing a decrease in electron amount emitted by the electron-emitting device. 
     However, the conventional electron-emitting device gradually decreases the electron emission amount along with long-term driving at a constant driving voltage. 
     In any type of electron-emitting device described above, the field strength near the electron-emitting portion is high during the actual driving. Changes over time near the electron-emitting portion arising from a high field strength is considered to decrease the electron emission amount. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electron-emitting device manufacturing method and driving method capable of suppressing changes over time in characteristics of an electron-emitting device and, more particularly, to provide an electron-emitting device manufacturing method and driving method capable of suppressing a decrease over time and unstableness in the electron emission amount from the electron-emitting device. 
     An electron-emitting device manufacturing method according to the present invention has the following steps. 
     That is, there is provided a method of manufacturing an electron-emitting device which has at least two electrodes and emits electrons by applying a voltage between the two electrodes, comprising: 
     the voltage application step of applying a voltage V 1  between the two electrodes, the voltage V 1  being a voltage having a relationship with a maximum voltage value V 2  applied to the electron-emitting device as a normal driving voltage after the voltage application step, so as to satisfy 
     giving a current I flowing upon application of a voltage V when the voltage V falling within a voltage range causing electron emission upon application of the voltage between the two electrodes is applied between the two electrodes: 
     
       
           I=f ( V )  (1) 
       
     
     and letting f′(V) be a differential coefficient of f(V) at the voltage V, 
     a first condition: 
     
       
           f ( V   1 ) /{V   1   ·f′ ( V   1 )−2 f ( V   1 )} &gt;f ( V   2 ) /{V   2   ·f′ ( V   2 )−2 f ( V   2 )}  (2) 
       
     
     wherein the voltage application step satisfies a second condition, upon completion of the voltage application step, 
     wherein the second condition is defined by letting Xn- 1  be a value of a right side, i.e., f(V 2 )/{V 2 ·f′(V 2 )−2f(V 2 )} of the inequality (2) upon a first application of the pulse-like voltage V 2  when the voltage V 2  is applied as pulses successively twice between the two electrodes upon completion of the voltage application step, and Xn be a value of the right side, i.e., f(V 2 )/{V 2 ·f′(V 2 )−2f(V 2 )} of the inequality (2) upon a second application of the pulse-like voltage V 2 , 
     wherein Xn- 1  and Xn satisfy: 
     
       
         ( Xn - 1   −Xn ) /Xn - 1 ≦0.02  (A) 
       
     
     The second condition is that Xn- 1  and Xn satisfy: 
     
       
         ( Xn - 1   −Xn ) /Xn - 1 ≦0.01  (B) 
       
     
     The electron-emitting device manufactured through the voltage application step hardly changes its characteristics upon long-time application of the maximum voltage value V 2  applied in actually driving the electron-emitting device (normally using it). The current I flowing upon application of the voltage V when the voltage V falling within a voltage range causing electron emission upon application of the voltage between the two electrodes is applied between the two electrodes is a current emitted upon application of the voltage V or a current flowing between the two electrodes. For example, in an FE or SCE type electron-emitting device, the current I is an emitted current or a current flowing between a pair of electrodes. 
     In an MIM type electron-emitting device, the current I is an emitted current or a current (diode current) flowing between two electrodes sandwiching an insulating layer. The differential coefficient f′(Vn) of f(Vn) at a given voltage Vn can be obtained as follows. An emission current (or a current flowing between two electrodes) In upon application of the voltage Vn, and an emission current (or a current flowing between the two electrodes) In 2  upon application of a voltage Vn 2  lower by a small amount dVn than the voltage Vn immediately after or immediately before application of the voltage Vn are obtained, and (In−In 2 ) is divided by dVn. That is, f(V)/{V·f′(V)−2f(V)} can be calculated as In/{Vn·(In−In 2 )/dVn−2In}. 
     Especially, the second condition is more preferably a condition that the change rate of Xn, i.e., (Xn- 1 −Xn)/Xn- 1  is 1% or less. 
     The voltage V 1  can be applied by various methods. The magnitude of the voltage V 1  is not necessarily constant as long as the voltage V 1  satisfies the condition of the inequality (2). The voltage V 1  is preferably applied as a pulse-like voltage. 
     To satisfy the second condition by the voltage application step, a voltage is applied under the same conditions as those adopted in applying the present invention, between two electrodes identical to two electrodes constituting at least part of an electron-emitting device to which the present invention is applied. Xn- 1  and Xn are measured for the electron-emitting device obtained in this step, thereby attaining conditions under which Xn- 1  and Xn satisfy the inequality (A), and more preferably the inequality (B). For example, when the voltage V 1  which satisfies the inequality (2) is applied as pulses a plurality of number of times in the voltage application step, the number of application times of the pulse voltage V 1  that can satisfy the second condition is obtained in advance, and the pulse-like voltage is applied the determined number of times in the voltage application step. Alternatively, the duration of the voltage application step that can satisfy the second condition may be obtained in advance, and the voltage application step may be performed for the determined duration. The voltage application step may also be performed while monitoring characteristics to directly or indirectly confirm whether the second condition is satisfied. For example, the second condition is confirmed to be satisfied when the left side of the inequality (2) i.e., the change rate of f(V 1 )/{V 1 ·f′(V 1 )−2f(V 1 )} reaches a predetermined value (e.g., 5% or 3%) or less in the voltage application step. In the voltage application step, the change rate of f(V 1 )/{V 1 ·f′(V 1 )−2f(V 1 )} is obtained every time, e.g., the pulse-like voltage V 1  is applied. If the change rate reaches the previously confirmed value or less, the voltage application step ends. Alternatively, the voltage V 2  may be actually applied between two electrodes during the voltage application step to confirm whether the second condition is satisfied. Until the second condition is confirmed to be satisfied, the voltage application step and the confirmation step by the application of the voltage V 2  may be repeated to realize the voltage application step which satisfies the second condition. 
     In the manufacturing method of the present invention, the voltage application step is preferably performed in a high-vacuum atmosphere. 
     In the manufacturing method of the present invention, when the two electrodes sandwich a gap, the voltage application step is preferably performed in an atmosphere in which the gap between the two electrodes is not made narrow by deposition of a substance in the atmosphere or a substance originating from the substance in the atmosphere in the voltage application step. 
     In the manufacturing method of the present invention, the voltage application step is preferably performed in an atmosphere in which carbon and a carbon compound in the atmosphere have a partial pressure of 1×10 −6  Pa or less. The partial pressure is more preferably 1×10 −8  Pa or less. The total pressure is preferably 1×10 −5  Pa or less, and more preferably 1×10 −6  Pa or less. 
     Assume that the second condition is satisfied if Xn- 1  and Xn satisfy (Xn- 1 −Xn)/Xn- 1 ≦0.02 or (Xn- 1 −Xn) /Xn- 1 ≦0.01 in the atmosphere upon the voltage application step. 
     As described above, two electrodes to which the voltage is applied in the voltage application step are a pair of electrodes of an FE type electron-emitting device (e.g., an emitter cone electrode and gate electrode for a Spindt type electron-emitting device), a pair of electrodes of an SCE type electron-emitting device (e.g., high- and low-potential electrodes), or a pair of electrodes sandwiching an insulating layer in an MIM type electron-emitting device. 
     The present invention can be preferably applied to an electron-emitting device such as an FE or SCE type electron-emitting device in which a gap is formed between two electrodes to which an electron emission voltage is applied. 
     The present invention incorporates an electron-emitting device manufacturing apparatus used in the electron-emitting device manufacturing method. This apparatus comprises a potential output portion for applying a voltage between the two electrodes. 
     An electron-emitting device driving method according to the present invention has the following steps. 
     That is, there is provided a method of driving an electron-emitting device which has at least two electrodes and emits electrons by applying a voltage between the two electrodes, 
     wherein the electron-emitting device undergoes the voltage application step of applying a voltage V 1  between the two electrodes, the driving method comprises a driving process of driving the electron-emitting device using a maximum value of a normal driving voltage as V 2 , the voltage V 1  is a voltage having a relationship with the voltage V 2  so as to satisfy 
     giving a current I flowing upon application of a voltage V when the voltage V falling within a voltage range causing electron emission upon application of the voltage between the two electrodes is applied between the two electrodes: 
     
       
           I=f ( V )  (1) 
       
     
     and letting f′(V) be a differential coefficient of f(V) at the voltage V, 
     a first condition: 
     
       
           f ( V   1 ) /{V   1   ·f′ ( V   1 )−2 f ( V   1 ) }&gt;f ( V   2 ) /{V   2   ·f′ ( V   2 )−2 f ( V   2 )}  (2) 
       
     
     the voltage application step includes the step of, upon completion of the voltage application step, 
     letting Xn- 1  be a value of f(V 2 )/{V 2 ·f′(V 2 )−2f(V 2 )} upon application of the pulse-like voltage V 2  when the voltage V 2  is applied as pulses successively twice between the two electrodes upon completion of the voltage application step, and Xn be a value of f(V 2 )/{V 2 ·f′(V 2 )−2f(V 2 )} upon next application of the pulse-like voltage V 2 , 
     satisfying a second condition that Xn- 1  and Xn satisfy: 
     
       
         ( Xn - 1   −Xn ) /Xn - 1 ≦0.02  (A) 
       
     
     The present invention incorporates an adjusting method used for adjustment before shipping in the voltage application step described as the voltage application step in the manufacturing method, or for adjustment after the start of actual use. 
     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in embodiments of the invention and constitute a part of the invention, serve to explain the principles of the invention together with the present specification. 
     FIG. 1 is a graph showing the plot of the electrical characteristics of an electron-emitting device to which the present invention can be applied; 
     FIG. 2 is a schematic sectional view showing an FE type electron-emitting device to which the present invention can be applied; 
     FIGS. 3A to  3 E are views showing the steps in manufacturing the FE type electron-emitting device to which the present invention can be applied; 
     FIG. 4 is a graph showing the electrical characteristics of an electron-emitting device formed in Example 1 and Example 2; 
     FIGS. 5A to  5 C are a schematic plan view and schematic sectional views, respectively, showing an SCE type electron-emitting device to which the present invention can be applied; 
     FIGS. 6A to  6 D are views showing the steps in manufacturing the SCE type electron-emitting device to which the present invention can be applied; 
     FIGS. 7A and 7B are graphs each showing a voltage pulse used during the manufacturing process of the SCE type electron-emitting device to which the present invention can be applied; 
     FIG. 8 is a graph showing the electrical characteristics of the SCE type electron-emitting device to which the present invention can be applied; 
     FIG. 9 is a graph showing the relationship between the emission current and device voltage of an electron-emitting device formed in Example 3; 
     FIG. 10 is a graph showing the relationship between the device current and device voltage of an electron-emitting device formed in Example 2; 
     FIGS. 11A to  11 C are graphs each showing a voltage waveform used in pre-driving of the present invention; and 
     FIG. 12 is a schematic sectional view showing an MIM type electron-emitting device to which the present invention can be applied. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. 
     A means for solving the above problems will be explained in detail. 
     FIG. 2 is a schematic view showing an example of an FE type electron-emitting device to which the present invention can be applied. 
     In FIG. 2, reference numeral  23  denotes a cathode;  24 , a gate electrode for emitting electrons from the cathode;  21 , an electrode for electrically connecting the cathode  23 ;  22 , an insulating layer for electrically insulating the cathode  23 , electrode  21 , and gate electrode  24 ; and  25 , an anode for capturing electrons emitted by the cathode  23 . 
     FIGS. 3A to  3 E are views showing a typical example of the arrangement and manufacturing method of the FE type electron-emitting device. 
     In FIGS. 3A to  3 E, a substrate  21  is made from a silicon substrate. An insulating layer  22  of silicon oxide is formed on the substrate  21  to a thickness of several hundred nm to several μm by thermal oxidization, sputtering, chemical vapor deposition, or the like. A gate electrode film of molybdenum or the like is formed to a thickness of several hundred nm to several μm by electron beam deposition or the like. A resist pattern corresponding to a prospective cathode formation position is formed on the gate electrode film using general lithography. An opening several hundred nm to several μm in diameter is formed in the gate electrode material by etching, thereby forming a gate electrode  24 . The insulating layer  22  at a position corresponding to the opening of the gate electrode  24  is removed with buffer hydrofluoric acid or the like. Then, the resist pattern is removed. While the substrate is rotated in a vacuum evaporator, a metal layer of aluminum or the like is diagonally deposited, and a cathode electrode material of molybdenum or the like is vertically deposited on the substrate to form a cathode  23 . The metal layer of aluminum or the like and the cathode electrode material formed on the gate electrode  24  are removed to complete an FE type electron-emitting device. 
     When an image display apparatus is to be manufactured using the FE type electron-emitting device, the anode  25  having fluorescent substances is arranged at a position apart from the surface having the cathode  23 , and a vacuum vessel incorporating these members is formed. 
     In the electron-emitting device prepared in this manner, a voltage is applied between the cathode  23  and the gate electrode  24  to emit electrons from the distal end of the cathode  23 . The emitted electrons are accelerated by the anode  25  to cause them to collide against the fluorescent substances formed on the anode  25 , thereby emitting light from the fluorescent substances on the anode  25 . At this time, the voltage applied between the cathode  23  and the gate electrode  24  is selected to make the cathode  23  serve as a low-potential side, and is set to a voltage (several ten V to several hundred V) at which electrons are emitted. The anode  25  is constituted by arranging fluorescent substances on, e.g., a transparent electrode formed on a glass substrate so as to externally emit light. An acceleration voltage (100 V to several kV or more) necessary for emitting light from the fluorescent substances is applied to the anode  25 . 
     One pixel is made up of a group of one or more FE type electron-emitting devices formed close to each other, and a fluorescent substance corresponding to the devices. In an image display apparatus having a plurality of pixels formed in a matrix, each pixel to be displayed is selected and driven, thereby displaying an image. 
     The FE type electron-emitting device with this structure to which the present invention can be applied has an electrical characteristic shown in FIG.  1 . 
     The abscissa in the graph of FIG. 1 represents the reciprocal of a voltage V applied between the cathode  23  and the gate electrode  24 , and the ordinate represents the logarithm of a value obtained by dividing a current I flowing between the cathode  23  and the anode  25  by the square of the voltage V. The electrical characteristic of the FE type electron-emitting device is plotted on this graph to generally draw a continuous line like the one plotted in FIG.  1 . 
     According to Fowler and Nordheim, the current I emitted by the FE type electron-emitting device, and the voltage V applied between the cathode and the gate have a relation: 
     
       
           I=A· ( β·V ) 2 ·exp( −B/ ( β·V ))  (4) 
       
     
     where A and B are constants depending on the material and emission area near the electron-emitting portion, and β is a parameter depending on the shape near the electron-emitting portion. The value obtained by multiplying the voltage V by β represents the field strength. 
     The qualitative value of β can be estimated by plotting log(I/V 2 ) with respect to  1 /V and calculating a gradient S of a straight line (broken line in FIG.  1 ). A value obtained by adding a negative sign to a value calculated by dividing the application voltage V by the gradient S of the approximate straight line: 
     
       
           −V/S   (5) 
       
     
     is obviously proportional to the strength of a field generated between the cathode  23  and the gate  24 . 
     This relationship is generalized. If the relationship between the emission current I and the voltage V is given by a function: 
     
       
           I=f ( V )  (6) 
       
     
     and f′(V) represents the differential coefficient of f(V), the field strength at the voltage V is proportional to 
     
       
           f ( V ) /{V·f′ ( V )−2 f ( V )}  (7) 
       
     
     This is defined as a field strength equivalent value. 
     The representative value of the field strength in the FE type electron-emitting device is as very high as 10 7  V/cm order. The value of the field strength applied to the insulating layer  22  is about 10 6  V/cm. 
     If long-period driving continues by a general method at a high field strength, constituent members irregularly change in the strong field, and the emission current value becomes unstable. 
     If such change irreversibly occurs, the emission current often decreases. This appears as a decrease in luminance in the image display apparatus. 
     Current unstableness during driving can be reduced by performing the voltage application step (to be referred to as “pre-driving” hereinafter) of the present invention prior to normal driving. 
     Pre-driving of the present invention is executed by, e.g., the following procedures. 
     Application voltages and emission currents at at least two different driving voltages for an electron-emitting device to be pre-driven, and the differential coefficients of the emission currents at these application voltages are obtained. For example, as shown in FIG. 4, f′(V 1 )=dI 1 /dV 1  is calculated from an emission current value I 1  corresponding to an application voltage V 1 , and an emission current change amount dI 1  upon slightly changing V 1  by dV 1 . Similarly, an emission current value I 2  corresponding to V 2 , and f′(V 2 )=dI 2 /dV 2  are calculated. 
     I 1  and I 2  are substituted into f(V) in equation (6) corresponding to the application voltages V 1  and V 2 , and values calculated by relation (7) are compared. When, for example, 
     
       
           I   1 /( V   1   ·dI   1 / dV   1 −2 ·I   1 ) &gt;I   2 /( V   2   ·dI   2 / dV   2 −2 ·I   2 )  (8) 
       
     
     is established, V 1  is adopted as a pre-driving voltage (to be referred to as Vpre hereinafter), and V 2  is adopted as a normal driving voltage (to be referred to as Vdrv hereinafter). In this case, the normal driving voltage means a voltage applied in using the electron-emitting device (or apparatus including it), and has a maximum value within a normal voltage application range in normal driving. 
     To the contrary, when 
     
       
           I   1 /( V   1   ·dI   1 / dV   1 −2· I   1 ) &lt;I   2 /( V   2   ·dI   2 / dV   2 −2 ·I   2 )  (9) 
       
     
     is established, V 2  is adopted as a pre-driving voltage (to be referred to as Vpre hereinafter), and V 1  is adopted as a normal driving voltage (to be referred to as Vdrv hereinafter). 
     By driving the electron-emitting device for a while at the pre-driving voltage Vpre calculated by this method, the electron-emitting portion serving as a main electron-emitting source at the voltage Vpre is driven by a high field strength. Accordingly, changes in constituent members causing unstableness can concentratedly appear within a short period to reduce variation factors. 
     When an inequality like the inequality (9) holds at voltages which satisfy V 1 &gt;V 2 , the normal driving voltage Vdrv is higher than the pre-driving voltage Vpre, and a higher field strength is applied to an electron-emitting portion (to be referred to as an electron-emitting portion A) changed at the voltage Vpre upon application of the voltage Vdrv. However, the main electron-emitting source which determines the electron emission amount at this time shifts to another electron-emitting portion (to be referred to as an electron-emitting portion B), and contribution of the electron-emitting portion A to the entire emission current is small. Even in this relationship, pre-driving is effective. By applying the voltage Vpre in advance, large variation factors at the electron-emitting portion A can be reduced in advance to prevent destructive variations at the driving voltage Vdrv. 
     Pre-driving desirably continues until the field strength in driving stabilizes. According to the experimental results by the present inventors, if pre-driving continues until the relative change rate of the field strength in pre-driving reaches 5% or less, the change rate of the field strength can be kept within about 5% even upon subsequent driving. The change rate of the field strength in application of an actual driving voltage, and particularly, the change rate of the field strength in the initial stage of application of an actual driving voltage can be reduced to satisfactorily realize the pre-driving effect. From the relation (7), pre-driving is continued until the change rate of the value of f(V 1 )/{V 1 ·f′(V 1 )−2f(V 1 )} reaches 5% or less. 
     In pre-driving, the voltage is applied while monitoring the change rate of the field strength in pre-driving. The pre-driving voltage can suitably use a pulse voltage. For example, the voltage is applied while the change rate of the field strength is calculated during a pulse idle time (time interval from application of a pulse voltage to application of the next pulse voltage). When the change rate reaches 5% or less, application of the voltage is stopped. 
     To monitor the change rate of the field strength in pre-driving, the following method can be employed. In pre-driving, the pre-driving voltage V 1 , and a voltage V 12  different from V 1  by a small voltage amount dV 1  are successively applied. Currents I 1  and I 12  flowing upon application of these voltages, and a difference dI 1  between I 1  and I 12  are obtained. Since f′(V 1 )=dI 1 /dV 1 , and f(V 1 )=I 1  from the equation (1), the field strength equivalent value f(V 1 )/{V 1 ·f′(V 1 )−2f(V 1 )} is rewritten into 
     
       
         Epre= I   1 /( V   1   ·dI   1 / dV   1 −2 ·I   1 )  (3) 
       
     
     The change rate of the field strength can, therefore, be obtained by monitoring the change rate of the value Epre. 
     As a voltage waveform in pre-driving, voltage waveforms as shown in FIGS. 11A,  11 B, and  11 C can be employed. FIG. 11A shows a voltage waveform representing that the voltage changes from a voltage V 1  to V 12  within a time period T 12  after the pre-driving voltage V 1  is applied for a time period T 1 . FIG. 11B shows a voltage waveform representing that the voltage V 12  is applied for the time period T 12  immediately after the pre-driving voltage V 1  is applied for the time period T 1 . FIG. 11C shows a voltage waveform representing that the voltage is off and then the voltage V 12  is applied for the time period T 12  after the pre-driving voltage V 1  is applied for the time period T 1 . The change rate of the value Epre is calculated from current values at the application voltages V 1  and V 12 , and pre-driving is continued until the change rate reaches 5% or less. 
     To suppress characteristic changes over time in normal long-period driving, the present invention adopts a condition that the change rate of the field strength equivalent value upon application of an actual use voltage is suppressed to 2% or less. For this purpose, in the above embodiment or following examples of the present invention, pre-driving continues until the change rate of the field strength equivalent value in pre-driving reaches 5% or less, and more preferably 3% or less. The pre-driving execution time for obtaining a given change rate of the field strength equivalent value in pre-driving changes depending on the difference between application voltage magnitudes in pre-driving and actual driving. For example, if the field strength equivalent value in pre-driving is set much higher than that in actual driving, short-time pre-driving can attain a change rate of 2% or less for the field strength equivalent value upon application of an actual use voltage. In this case, however, the device characteristics may greatly degrade, or the device may be destroyed. For this reason, the pre-driving voltage is preferably set such that the change rate of the field strength equivalent value does not extremely exceed 10% at the start of pre-driving. 
     This voltage application step of the present invention is also effective for electron-emitting devices such as SCE and MIM type electron-emitting devices, in addition to the FE type electron-emitting device. 
     An SCE (Surface-Conduction) type of electron-emitting device to which the present invention can be applied will be described with reference to FIGS. 5A to  5 C. 
     The basis structures of surface-conduction type of electron-emitting devices to which the present invention can be applied are mainly classified into flat and step electron-emitting devices. 
     First, a flat surface-conduction type of electron-emitting device will be described. 
     FIGS. 5A to  5 C are schematic views showing the structure of a flat surface-conduction type of electron-emitting device to which the present invention can be applied. FIG. 5A is a plan view, and FIG. 5B is a sectional view. 
     In FIGS. 5A to  5 C, reference numeral  51  denotes a substrate;  52  and  53 , device electrodes;  54 , a conductive thin film; and  55 , an electron-emitting portion. 
     Examples of the substrate  51  are a silica glass substrate, a glass substrate having a low impurity content such as an Na substrate, a soda-lime glass, a glass substrate prepared by stacking an SiO 2  layer on a soda-lime glass by sputtering or the like, a ceramics substrate such as an alumina substrate, an Si substrate, and the like. 
     An example of a material for the facing device electrodes  52  and  53  is a general conductive material. The general conductive material includes metals such as Ni, Cr, Au, Mo, W, Pt, Ti, Al, Cu, and Pd, or alloys of these metals, metals such as Pd, Ag, Au, RuO 2 , and Pd—Ag, a printed conductor made of a metal oxide and glass or the like, a transparent conductor such as In 2 O 3 —SnO 2 , and a semiconductor material such as polysilicon. 
     A device electrode interval L, a device electrode width W, the shape of the conductive thin film  54 , and the like are appropriately designed in accordance with an application purpose or the like. The device electrode interval L can be set within the range from several hundred nm to several hundred μm, and preferably the range from several μm to several ten μm. 
     The device electrode width W can be set within the range from several μm to several hundred μm in consideration of the resistance value of the electrode and electron-emitting characteristics. A film thickness d of the electrodes  52  and  53  can be set within the range from several ten nm to several μm. 
     Note that the surface-conduction type of electron-emitting device is not limited to the structure shown in FIGS. 5A to  5 C, and can be constituted by sequentially stacking the conductive thin film  54  and the facing device electrodes  52  and  53  on the substrate  51 . 
     The conductive thin film  54  preferably comprises a fine particle film made of fine particles in order to obtain good electron-emitting characteristics. The thickness of the conductive thin film  54  is properly set in consideration of step coverage for the device electrodes  52  and  53 , the resistance value between the device electrodes  52  and  53 , forming conditions (to be described later), and the like. This thickness is set preferably to the range from several hundred pm to several hundred nm, and more preferably to the range from 1 nm to 50 nm. A resistance value Rs is 10 2  to 10 7  Ω/_. Note that Rs appears when a resistance R of a thin film having a thickness t, a width w, and a length l is given by R=Rs (l/w). The present specification will exemplify electrification processing as forming processing, but the forming processing is not limited to this and includes processing of forming a fissure in a film and realizing a high-resistance state. 
     Examples of a material for the conductive thin film  54  are metals such as Pd, Pt, Ru, Ag, Au, Ti, In, Cu, Cr, Fe, Zn, Sn, Ta, W, and Pb, oxides such as PdO, SnO 2 , In 2 O 3 , PbO, and Sb 2 O 3 , borides such as HfB 2 , ZrB 2 , LaB 6 , CeB 6 , YB 4 , and GdB 4 , carbides such as TiC, ZrC, HfC, TaC, SiC, and WC, nitrides such as TiN, ZrN and HfN, semiconductors such as Si and Ge, and carbons. 
     The fine particle film is one containing a plurality of fine particles. As the fine structure, individual fine particles may be dispersed, be adjacent to each other, or overlap each other (including that masses of fine particles form an island structure as a whole). One fine particle has a diameter within the range from several multiples of 0.1 nm to several hundred nm, and preferably the range from 1 nm to 20 nm. 
     The electron-emitting portion  55  has a high-resistance fissure formed at part of the conductive thin film  54 . The electron-emitting portion  55  depends on the thickness, quality, and material of the conductive thin film  54 , a forming method (to be described later), and the like. The electron-emitting portion  55  may contain conductive fine particles each having a diameter within the several multiples of 0.1 nm to several ten nm. The conductive fine particles contain some or all of elements of a material forming the conductive thin film  54 . Carbon and a carbon compound are contained in the electron-emitting portion  55  and the neighboring conductive thin film  54 . 
     Next, a step surface-conduction type of electron-emitting device will be described. 
     FIG. 5C is a schematic view showing an example of a step surface-conduction type of electron-emitting device to which the surface-conduction type of electron-emitting device of the present invention can be applied. 
     In FIG. 5C, the same reference numerals as in FIGS. 5A and 5B denote the same parts. Reference numeral  56  denotes a step-forming member. A substrate  51 , device electrodes  52  and  53 , a conductive thin film  54 , and an electron-emitting portion  55  can be made of the same materials as in the above-mentioned flat surface-conduction type of electron-emitting device. The step-forming member  56  can be made of an insulating material such as SiO 2  formed by vacuum evaporation, printing, sputtering, and the like. The thickness of the step-forming member  56  corresponds to the device electrode interval L of the flat surface-conduction type of electron-emitting device and can be set within the range from several hundred nm to several ten μm. This thickness is set in consideration of the manufacturing method of the step-forming member and a voltage applied between the device electrodes, and preferably set within the range from several ten nm to several μm. 
     After the device electrodes  52  and  53  and step-forming member  56  are formed, the conductive thin film  54  is stacked on the device electrodes  52  and  53 . In FIG. 5C, the electron-emitting portion  55  is formed on the step-forming member  56 . The electron-emitting portion  55  depends on manufacturing conditions, forming conditions, and the like, and its shape and position are not limited to those in FIG.  5 C. 
     The surface-conduction type of electron-emitting device can be manufactured by various methods, and an example of the methods is schematically shown in FIGS. 6A to  6 D. 
     An example of the manufacturing method will be explained with reference to FIGS. 5A,  5 B, and  6 A to  6 D. Also in FIGS. 6A to  6 D, the same reference numerals as in FIGS. 5A and 5B denote the same parts. 
     1) A substrate  51  is satisfactorily cleaned with a detergent, pure water, an organic solvent, or the like, and a device electrode material is deposited by vacuum evaporation, sputtering, or the like to form device electrodes  52  and  53  on the substrate  51  by, e.g., photolithography (FIG.  6 A). 
     2) The substrate  51  having the device electrodes  52  and  53  is coated with an organic metal solvent to form an organic metal thin film. As the organic metal solvent, an organic metal compound solvent containing a metal of a material for the conductive thin film  54  as a main element can be used. The organic metal thin film is heated, sintered, and patterned into a conductive thin film  54  by etching, or lift-off using a mask  57  corresponding to the conductive thin film shape, as shown in FIG. 6B (FIG.  6 C). Although the coating method of the organic metal solvent has been exemplified, the formation method of the conductive thin film  54  is not limited to this, and can be vacuum evaporation, sputtering, chemical vapor deposition, dispersion coating, dipping, spinner method, or the like. Alternatively, the conductive thin film  54  can be directly patterned by an ink-jet method or the like. 
     3) The obtained device undergoes a forming step. As an example of the forming method, an electrification method in a vacuum vessel will be described with reference to FIG.  6 D. 
     In FIG. 6D, reference numeral  61  denotes a vacuum vessel which is evacuated through a gate valve  62  by a vacuum pump  63  such as a turbo molecular pump, sputter-ion pump, or cryopump. If necessary, the vacuum pump  63  is connected to an auxiliary pump  64  such as a scroll pump, rotary pump, or sorption pump. Reference numeral  66  denotes a container for containing activation gas used in an activation step (to be described below) The container  66  is connected to the vacuum vessel  61  through an adjustment valve  65  such as a variable-leakage valve or needle valve. 
     The device electrodes  52  and  53  are connected to a voltage application means. For example, as shown in FIG. 6D, the device electrode  52  is connected to a ground potential, and the device electrode  53  is connected to a power supply  67  through a current supply terminal. To monitor a current value flowing between the device electrodes  52  and  53 , an ammeter  68  is connected. Reference numeral  58  denotes an anode electrode used in a subsequent step. The anode electrode  58  is connected to a high-voltage power supply  69  through an ammeter  70 . 
     After the vacuum vessel is evacuated, the device electrodes  52  and  53  are electrified using the power supply  67  to form an electron-emitting portion  55  having a changed structure at a portion of the conductive thin film  54  (FIG.  6 D). According to forming processing, a structure-changed portion such as a locally destructed, deformed, or quality-changed portion is formed in the conductive thin film  54 . This portion functions as the electron-emitting portion  55 . FIGS. 7A and 7B show examples of a forming voltage waveform. 
     This voltage waveform is preferably a pulse waveform. Pulses can be applied by a method, FIG. 7A, of applying voltage pulses while increasing the pulse peak value, or a method, FIG. 7B, of successively applying pulses whose peak value is a constant voltage. 
     T 1  and T 2  in FIG. 7A represent the pulse width and interval of the voltage waveform, respectively. In general, T 1  is set within the range from 1 μsec to 10 msec, and T 2  is set within the range from 10 μsec to 1 sec. The pulse peak value can be increased every step of, e.g., about 0.1 V. The end of forming processing can be determined by detecting a change in resistance value caused when the conductive thin film  52  is locally destructed or deformed. For example, the end of forming processing can be detected by applying a voltage so as not to locally destruct or deform the conductive thin film  52  during the pulse interval T 2  and measuring the current. A device current flowing upon application of a voltage of about 0.1 V is measured to obtain the resistance value, and when the resistance value exhibits 1 MΩ or more, forming processing is completed. 
     The pulse waveform is not limited to a rectangular waveform, and can adopt a desired waveform such as a triangular waveform. 
     T 1  and T 2  in FIG. 7B can be set similarly to those shown in FIG.  7 A. The pulse peak value is appropriately selected in accordance with the structure of the surface-conduction type of electron-emitting device. Under these conditions, a voltage is applied for, e.g., several sec to several ten min. The pulse waveform is not limited to a rectangular waveform, and can adopt a desired waveform such as a triangular waveform. By this step, a gap is formed in the conductive film. 
     4) The device having undergone forming processing is preferably subjected to processing called an activation step. In the activation step, a device current If and an emission current Ie greatly change. 
     Similar to forming processing, the activation step is executed by repeatedly applying pulses in an atmosphere containing an organic substance gas. This atmosphere can be formed using an organic gas left in an atmosphere when the vacuum vessel is evacuated with an oil diffusion pump, rotary pump, or the like, or using a proper organic substance gas introduced into a vacuum in the vacuum vessel temporarily sufficiently evacuated by an ion pump or the like. The gas pressure of a preferable organic substance changes depending on the application purpose of the device, the shape of the vacuum vessel, the kind of organic substance, and the like, and is appropriately set in accordance with them. Examples of the proper organic substance are aliphatic hydrocarbons such as alkane, alkene, alkyne, aromatic hydrocarbons, alcohols, aldehydes, ketones, amines, phenol, and organic acids such as carboxylic acid and sulfonic acid. Detailed examples are saturated hydrocarbons such as methane, ethane, and propane, unsaturated hydrocarbons such as ethylene and propylene, butadiene, n-hexane, 1-hexene, benzene, toluene, o-xylene, benzonitrile, trinitrile, chloroethylene, trichloroethylene, methanol, ethanol, isopropanol, formaldehyde, acetaldehyde, acetone, methyl ethyl ketone, diethyl ketone, methyl amine, ethyl amine, acetic acid, propionic acid, and a mixture of them. By this processing, carbon or a carbon compound is deposited on the device, and particularly in the gap from the organic substance present in the atmosphere. As a result, the device current If and emission current Ie greatly change. 
     The end of the activation step is determined while measuring the device current If and emission current Ie. Note that the pulse width, pulse interval, pulse peak value, and the like are appropriately set. 
     5) The electron-emitting device obtained by these steps is desirably subjected to a stabilization step. In this step, the organic substance in the vacuum vessel is exhausted. An evacuation apparatus for evacuating the vacuum vessel is preferably one not using any oil so as not to affect device characteristics by an organic substance such as oil produced by the apparatus. For example, this evacuation apparatus is a magnetic levitation type turbo molecular pump, cryopump, sorption pump, ion pump, or the like. 
     When the activation step uses an oil diffusion pump or rotary pump as an exhaust device, and uses an organic gas originating from an oil component produced by the pump, the partial pressure of the component must be suppressed as low as possible. The partial pressure of the organic component in the vacuum vessel is preferably 1×10 −6  Pa or less, and more preferably 1×10 −8  Pa or less so as not to newly deposit any carbon or carbon compound. In evacuating the vacuum vessel, the whole vacuum vessel is preferably heated to facilitate exhaustion of organic substance molecules attached to the inner wall of the vacuum vessel and the electron-emitting device. This heating is desirably done at a temperature of 80 to 250° C. and preferably 150° C. or more for a time as long as possible. However, the heating conditions are not particularly limited to them. Heating is performed under conditions properly selected in consideration of various conditions such as the size and shape of the vacuum vessel and the structure of the electron-emitting device. The internal pressure of the vacuum vessel must be minimized, and is preferably 1×10 −5  Pa or less, and more preferably 1×10 −6  Pa or less. 
     A drive atmosphere after the stabilization step preferably maintains an atmosphere at the end of the stabilization step, but is not limited to this. As far as the organic substance is satisfactorily removed, stable characteristics can be maintained to a certain degree even if the pressure of the vacuum vessel slightly rises. 
     By adopting such vacuum atmosphere, deposition of new carbon or carbon compound can be suppressed, and H 2 O and O 2  attached to the vacuum vessel and substrate can be removed. As a result, the device current If and emission current Ie relatively stabilize. 
     The basic characteristics of the electron-emitting device obtained by the above steps to which the present invention can be applied will be described with reference to FIG.  8 . 
     FIG. 8 is a graph schematically showing the relationship between the emission current Ie, device current If, and device voltage Vf measured using the vacuum processing device shown in FIG.  6 D. In measurement, a high voltage was applied from the high-voltage power supply  69  to the anode electrode  58  arranged above the electron-emitting device. For example, measurement can be done at an anode electrode voltage of 1 kV to 10 kV, and a distance H of 2 mm to 8 mm between the anode electrode and the electron-emitting device. In FIG. 8, since the emission current Ie is much smaller than the device current If, they are given in arbitrary units. Note that both the ordinate and abscissa are based on linear scales. 
     As is apparent from FIG. 8, the electron-emitting device to which the present invention can be applied has three characteristic features regarding the emission current Ie: 
     (i) The emission current Ie abruptly increases when a device voltage of a predetermined level (to be referred to as a threshold voltage: Vth in FIG. 8) or higher is applied to the device, but almost no emission current Ie is detected when the voltage is equal to or lower than the threshold voltage Vth. The device is a nonlinear device having a clear threshold voltage Vth with respect to the emission current Ie. 
     (ii) The emission current Ie can be controlled by the device voltage Vf because the emission current Ie linearly depends on the device voltage Vf. 
     (iii) Emission charges captured by the anode electrode  58  depend on the application time of the device voltage Vf. In other words, a charge amount captured by the anode electrode  58  can be controlled by the application time of the device voltage Vf. 
     As is apparent from the above description, the electron-emitting characteristics of the surface-conduction type of electron-emitting device to which the present invention can be applied can be easily controlled in accordance with an input signal. By using this property, the surface-conduction type of electron-emitting device can be applied to various devices such as an electron source constituted by arranging a plurality of electron-emitting devices, and an image forming device. 
     The relationship between the emission current Ie and the device voltage Vf for the surface-conduction type of electron-emitting device to which the present invention can be applied is plotted on the graph shown FIG. 1 to exhibit a characteristic which can be approximated by an almost straight line. For the device current, the relationship between If and Vf is plotted on the graph of FIG. 1 to exhibit a characteristic having a region which can be approximated by a straight line, as represented by a continuous line in FIG.  1 . 
     Pre-driving for the surface-conduction type of electron-emitting device can also employ the similar method to the FE type electron-emitting device. 
     In this case, as shown in FIG. 9, the voltages V 1  and V 2  in the inequalities (8) and (9) are replaced by device voltages Vf 1  and Vf 2 . Similarly, the emission currents are replaced by Ie 1  and Ie 2 . 
     When the surface-conduction type of electron-emitting device is used, not only the relationship between the driving voltage and the emission current, but also the relationship between the driving voltage and the device current can be used as a reference for setting pre-driving conditions. 
     In this case, as shown in FIG. 10, the voltages V 1  and V 2  in the inequalities (8) and (9) are replaced by the device voltages Vf 1  and Vf 2 . Similarly, the device currents are replaced by If 1  and If 2 . 
     The voltage application step of the present invention can also be applied to an MIM type electron-emitting device as shown in FIG.  12 . 
     In FIG. 12, reference numeral  121  denotes a substrate;  122 , a lower electrode;  123 , an insulating thin film;  124 , an upper electrode; and  125 , an electron-emitting portion. 
     By applying a voltage between the lower and upper electrodes  122  and  124 , electrons emitted by the lower electrode  122  are accelerated within the insulating thin film  123 , and emitted from the electron-emitting portion  125  through the upper electrode  124 . 
     A method of manufacturing the MIM type electron-emitting device will be briefly described. 
     A metal material is deposited on a substrate  122  by a film formation method such as vapor deposition or sputtering, thereby forming a lower electrode  122 . 
     By the same film formation method, an insulating thin film  123  is formed on the lower electrode  122 . Examples of a material for the insulating thin film  123  are oxides such as Al 2 O 3 , MnO 2 , and SiO 2 , halides such as LiF, KF, MgF 2 , and NaBr, and sulfides such as ZnS and CdS. A proper film thickness of the insulating thin film  123  is several nm to several hundred nm. 
     By the same film formation method as described above, an upper electrode  124  is formed on the insulating thin film  123 . Examples of a material for the upper electrode  124  are Au, Cu, Ag, and Al. After the MIM type electron-emitting device is formed in this manner, forming processing is done by applying a voltage between the lower and upper electrodes  123  and  124  so as to make the upper electrode  124  positive. By this forming processing, the electron-emitting portion  125  emits electrons. 
     Also in the MIM type electron-emitting device, the voltage applied between the upper and lower electrodes, the emission current emitted from the electron-emitting portion between the two electrodes, and the diode current flowing through the two electrodes exhibit the same relationships as in FIGS. 9 and 10. Therefore, the MIM type electron-emitting device can be pre-driven by the same method as for the FE and SCE type electron-emitting devices. 
     Note that pre-driving is executed in the last stage of the manufacturing process, e.g., after or during the stabilization step. Alternatively, pre-driving can be done as a refresh step before shipping after stock, or as a proper refresh mode after the electron-emitting device is used. 
     EXAMPLES 
     Examples of the present invention will be described. However, the present invention is not limited to these examples, and incorporates replacement of respective elements and design change as far as the object of the present invention is achieved. 
     Example 1 
     In Example 1, the voltage application step (pre-driving) of the present invention is applied to an FE type electron-emitting device having the same structure as that schematically shown in FIG. 2. A plurality of electron-emitting devices (devices A, B, C, D, and E) were manufactured by the following steps. The electron-emitting device manufacturing method used in Example 1 will be explained with reference to FIGS. 3A to  3 E. 
     Step-1a (FIG. 3A) 
     A 1.5-μm thick insulating layer  22  of silicon oxide was formed on a cleaned silicon substrate  21  by thermal oxidization, and a 0.4-μm thick molybdenum film was formed by electron beam deposition. A resist (PMM: Poly-Methyl-Methacrylate) was applied to the molybdenum film, and irradiated with a converged electron beam to form a pattern corresponding to the opening of a gate electrode. A 1.5-μm φ opening was formed in the gate electrode material by etching, thereby forming a gate electrode  24 . The insulating layer  22  at a position corresponding to the opening of the gate electrode  24  was removed with buffer hydrofluoric acid. In Example 1, a total of nine gate electrode openings were formed. 
     Step-1b (FIG. 3B) 
     The resist pattern was removed, and aluminum  26  was diagonally deposited while the substrate was rotated in the vacuum evaporator. 
     Step-1c (FIG. 3C) 
     Molybdenum was vertically deposited on the substrate to form a cathode  23 . 
     Step-1d (FIG. 3D) 
     The aluminum  26  and molybdenum deposited on the gate electrode  24  were removed to complete an FE type electron-emitting device. 
     The electron-emitting device completed in this manner was set in a vacuum vessel, and underwent pre-driving of the present invention to check electron-emitting characteristics. 
     FIG. 3E is a sectional view schematically showing this state. Reference numerals  21  to  24  denote the components of the electron-emitting device formed up to step-1d. Reference numeral  25  denotes an anode electrode arranged 5 mm above the electron-emitting device. The anode electrode is constituted by forming an ITO transparent electrode and fluorescent substances on a glass substrate. Reference numeral  31  denotes a vacuum vessel which is evacuated by a turbo molecular pump  33  through a gate valve  32 . The turbo molecular pump is evacuated by a scroll pump  34 . In the electron-emitting device, the electrode  21  made from the silicon substrate is connected to a ground potential, the gate electrode  24  is connected to a power supply  35  through a current supply terminal, and the anode electrode  25  is connected to a high-voltage power supply  36  through a current supply terminal. An emission current flowing through the anode electrode is measured by an ammeter  37 . 
     In the arrangement shown in FIG. 3E, the vacuum vessel  31  was evacuated to an internal pressure of 1×10 −4  Pa, and the whole vacuum vessel  31  and electron-emitting device were temporarily heated to 250° C. for 10 hrs using a heater (not shown). The vacuum vessel  31  was kept evacuated to set the internal pressure of the vacuum vessel at room temperature to about 1×10 −7  Pa. 
     After the internal pressure of the vacuum vessel was adjusted, pre-driving as the feature of the present invention was performed. 
     In pre-driving, the anode voltage was set to 1,000 V, two different voltages were applied to the gate electrode, and electrical characteristics at two comparison points (◯ and  in FIG. 4) on the plot of FIG. 4 were obtained. 
     More specifically, an emission current value I 1  flowing at V 1 =200 V, and a change amount dI 1  of current flowing when V 1  was changed by dV 1 =10 V were obtained. A differential coefficient dI 1 /dV 1  of the current at the voltage V 1  was calculated. Similarly, an emission current I 2  flowing at a voltage V 2 =160 V different from V 1 , and dI 2  for dV 2 =5 V were obtained. A differential coefficient dI 2 /dV 2  of the current at the voltage V 2  was calculated. Consequently, a relation: 
     
       
           I   1 /( V   1   dI   1 / dV   1 −2· I   1 ) &gt;I   2 /( V   2   ·dI   2 / dV   2 −2· I   2 ) 
       
     
     was obtained, and V 1  was adopted as the pre-driving voltage Vpre. 
     At the obtained pre-driving voltage Vpre=200 V, the electron-emitting devices (devices A, B, C, and D) were pre-driven. At this time, the driving voltage waveform was a waveform shown in FIG. 11B, and V 1 =200 V, V 12 =190 V, T 1 =0.2 msec, T 12 =0.05 msec, and the pulse interval T 2 =16.7 msec were used. 
     During pre-driving, the current I 1  at V 1  and the current I 12  at V 12  were measured. From the difference dI 1  between I 1  and I 12 , and the difference dV 1  between V 1  and V 12 , 
     
       
         Epre =I   1 /( V   1   ·dI   1 / dV   1 −2· I   1 ) 
       
     
     was calculated to perform pre-driving. 
     Pre-driving continued until the change rate of the value Epre reached about 10% for the device A, until the change rate of the value Epre reached about 7% for the device B, until the change rate of the value Epre reached about 5% for the device C, and until the change rate of the value Epre reached about 3% for the device D. No pre-driving was done for the device E. 
     The voltage was set to V 2 =160 V, and the devices were driven for a long time. Changes over time and variations in emission current during driving were the largest in the device E not pre-driven, and the second and third largest in the devices A and B. In the devices C and D, the emission current during driving hardly decreased and varied, and stable electron-emitting characteristics were attained. 
     A 160-V voltage pulse was applied to the devices C and D successively twice, and their field strength equivalent values were checked to find that the change rates of the field strength equivalent values were 2% or less. In particular, the device D exhibited a change rate lower than 1%. 
     Example 2 
     In Example 2, the voltage application step of the present invention is applied to an SCE type electron-emitting device having the same structure as that schematically shown in FIGS. 5A to  5 C. A plurality of electron-emitting devices (devices F, G, H, I, and J) were manufactured by the following steps. The electron-emitting device manufacturing method used in Example 2 will be explained with reference to FIGS. 6A to  6 D. 
     Step-3a (FIG. 6A) 
     A quartz substrate  51  was cleaned, and Ti and Pt were deposited on the substrate  51  to thicknesses of 5 nm and 50 nm, respectively. A photoresist was applied to the deposition film to form a pattern conforming to a pair of device electrodes  52  and  53 . Pt and Ti were etched away from unwanted portions, and the resist was removed to form device electrodes  52  and  53  on the substrate  51 . Note that an interval L between the device electrodes  52  and  53  was 10 μm, and a length W of the device electrode was 300 μm. ps Step-3b (FIG. 6B) 
     A 50-nm thick Cr film was deposited by vacuum deposition on the substrate  51  having the device electrodes  52  and  53 . An opening corresponding to the prospective formation portion of a conductive thin film was formed in the Cr film by photolithography. An organic Pd compound solution (ccp-4230: available from Okuno Seiyaku KK) was applied, and the resultant structure was heated in atmosphere at 300° C. 
     Step-3c (FIG. 6C) 
     The Cr film formed in step-3b was wet-etched. The structure was cleaned with pure water and dried to form a conductive thin film  54 . 
     The following steps were performed after the electron-emitting device during the manufacturing process was set in a vacuum vessel and electrically connected, as shown in FIG.  6 D. 
     As shown in FIG. 6D, the device electrode  52  was connected to the ground potential, and the device electrode  53  was connected to an ammeter  68  and device voltage power supply  67  through a current supply terminal. An anode electrode  58  was arranged 5 mm above the substrate  51 . The anode electrode  58  was connected to an ammeter  70  and high-voltage power supply  69  through a current supply terminal. 
     Step-3d 
     The vacuum vessel  61  was evacuated to about 1×10 −3  Pa or less using a scroll pump  64  and turbo molecular pump  63 . The device electrode  53  received a voltage generated by the device voltage power supply  67  serving as a means for applying a potential to one of the two electrodes constituting the device, thereby applying a voltage between the two electrodes. Forming processing was done to form an electron-emitting portion  55 . The applied voltage was a pulse-like voltage as shown in FIG. 7A, which asymptotically increased its peak value with the lapse of time. The pulse width T 1  was 1 msec, and the pulse interval T 2  was 16.7 msec. When the pulse peak value reached 6 V during forming processing, a current value flowing through the ammeter  68  greatly decreased. The pulse voltage was kept applied until the pulse peak value reached 6.5 V. After that, application of the voltage was stopped. The resistance value between the device electrodes  52  and  53  was measured to exhibit 1 MΩ or more. Thus, forming processing ended. 
     Step-3e 
     The vacuum vessel  61  was kept evacuated to decrease its internal pressure to 10 −5  Pa or less. A variable-leakage valve  65  was adjusted to introduce benzonitrile gas from an activation gas container  66  to the vacuum vessel  61 , thereby performing the activation step. In the activation step, the internal pressure of the vacuum vessel containing the activation gas was adjusted to 10 −4  Pa, and a voltage generated by the device voltage power supply  67  was applied to the device electrode  53 . The applied voltage was a pulse-like voltage as shown in FIG. 7B, which had a constant peak value. The pulse peak value was 16 V, the pulse width T 1  was 1 msec, and the pulse interval T 2  was 16.7 msec. After activation processing continued one hour, application of the voltage was stopped, introduction of the activation gas was stopped, and the activation gas was exhausted from the vacuum vessel. 
     Step-3f 
     The whole vacuum vessel  61  and electron-emitting device were temporarily heated to 250° C. for 10 hrs using a heater (not shown). The vacuum vessel was kept evacuated to set the internal pressure of the vacuum vessel at room temperature to about 1×10 −7  Pa. 
     After the internal pressure of the vacuum vessel was adjusted, pre-driving as the feature of the present invention was performed. 
     In pre-driving, the anode voltage was set to 0 V, two different voltages were applied to the device electrode  53 , and electrical characteristics at two comparison points (◯ and  in FIG. 10) on the plot of FIG. 10 were obtained. 
     More specifically, a device current value If 1  flowing at Vf 1 =16.0 V, and a change amount dIf 1  of current flowing when Vf 1  was changed by dVf 1 =0.2 V were obtained. A differential coefficient dIf 1 /dVf 1  of the current at the voltage Vf 1  was calculated. Similarly, a device current If 2  flowing at a voltage Vf 2 =14.5 V different from Vf 1 , and dIf 2  for dVf 2 =0.2 V were obtained. A differential coefficient dIf 2 /dVf 2  of the current at the voltage Vf 2  was calculated. Consequently, a relation: 
     
       
           If   1 /( Vf   1   ·dIf   1 / dVf   1 −2· If   1 ) &gt;If   2 /( Vf   2   ·dIf   2 / dVf   2 −2· If   2 ) 
       
     
     was obtained, and Vf 1  was adopted as the pre-driving voltage Vpre. 
     At the obtained pre-driving voltage Vpre=16 V, the electron-emitting devices (devices F, G, H, and I) were pre-driven. At this time, the driving voltage waveform was a waveform shown in FIG. 11B, and V 1 =16 V, V 12 =15.7 V, T 1 =0.5 msec, T 2 =0.05 msec, and the pulse interval T 3 =16.7 msec were used. 
     During pre-driving, the current I 1  at V 1  and the current I 12  at V 12  were measured. While Epre=I 1 /(V 1 ·dI 1 /dV 1 −2·I 1 ) was calculated from the difference dI 1  between I 1  and I 12 , and the difference dV 1  between V 1  and V 12 , pre-driving was executed. 
     Pre-driving continued until the change rate of the value Epre reached about 10% for the device F, until the change rate of the value Epre reached about 7% for the device G, until the change rate of the value Epre reached about 5% for the device H, and until the change rate of the value Epre reached about 3% for the device I. No pre-driving was done for the device J. 
     The driving voltage V 2  was set to 14.5 V, the anode voltage was set to 1,000 V, and the devices were driven for a long time. Changes over time and variations in emission current during driving were the largest in the device J not pre-driven, and the second and third largest in the devices F and G. In the devices H and I, the emission current during  62  driving hardly decreased and varied, and stable electron-emitting characteristics were attained. 
     A 14.5-V voltage pulses was applied to the devices H and I successively twice, and their field strength equivalent values were checked to find that the change rates of the field strength equivalent values were 1% or less. 
     Example 3 
     Example 3 used electron-emitting devices (devices K, L, M, N, and O) prepared with the same structure by the same manufacturing method as those of the electron-emitting devices prepared in Example 2. 
     These electron-emitting devices were set in a proper vacuum atmosphere, and underwent the following processing, similar to Example 2. 
     In pre-driving, the anode voltage was set to 1,000 V, two different voltages were applied to a device electrode  53 , and electrical characteristics at two comparison points (◯ and  in FIG. 9) on the plot of FIG. 9 were obtained. Note that the method of deriving the differential coefficient of an emission current corresponding to the application voltage was the same as in Example 2 except that the emission current replaced the device current, and a description thereof will be omitted. 
     A device current Ie 1  flowing at Vf 1 =15.5 V, and the differential coefficient of the emission current were obtained. A device current Ie 2  flowing at Vf 2 =14.3 V, and the differential coefficient of the emission current were obtained. As a result, a relation: 
     
       
           Ie   1 /( Vf   1   ·dIe   1 / dVf   1 −2· Ie   1 ) &gt;Ie   2 /( Vf   2   ·dIe   2 / dVf   2 −2 ·Ie   2 ) 
       
     
     was obtained, and Vf 1  was adopted as the pre-driving voltage Vpre. 
     At the obtained pre-driving voltage Vpre=15.5 V, the electron-emitting devices were pre-driven. At this time, the driving voltage waveform was a waveform shown in FIG. 11C, and V 1 =15.5 V, V 12 =15.0 V, T 1 =0.2 msec, T 12 =0.1 msec, the pulse interval T 2 =16.7 msec, and the pulse interval T 22 =0.05 msec were used. 
     During pre-driving, the current I 1  at V 1  and the current I 12  at V 12  were measured. While Epre=I 1 /(V 1 ·dI 1 /dV 1 −2·I 1 ) was calculated from the difference dI 1  between I 1  and I 12 , and the difference dV 1  between V 1  and V 12 , pre-driving was executed. 
     Pre-driving continued until the change rate of the value Epre reached about 9% for the device K, until the change rate of the value Epre reached about 7% for the device L, until the change rate of the value Epre reached about 5% for the device M, and until the change rate of the value Epre reached about 3% for the device N. No pre-driving was done for the device O. 
     The driving voltage V 2  was set to 14.3 V, the anode, voltage was set to 1,000 V, and the devices were driven for a long time. Changes over time and variations in emission current during driving were the largest in the device O not pre-driven, and the second and third largest in the devices K and L. In the devices M and N, the emission current during driving hardly decreased and varied, and stable electron-emitting characteristics were attained. 
     A 14.3-V voltage pulses was applied to the devices M and N successively twice, and their field strength equivalent values were checked to find that the change rates of the field strength equivalent values were 2% or less. In particular, the device N exhibited a change rate lower than 1%. 
     As has been described above, the present invention can realize stable electron emission almost free from decrease and variations in emission current during normal driving. 
     The embodiment of the present invention has been described above. As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.