Abstract:
A thin film resistor maintains its resistance value when stress is applied so that it may be used in a high precision bleeder resistor circuit to maintain an accurate voltage dividing ratio. The thin film resistor has a P-type thin film resistor formed of a P-type semiconductor thin film and an N-type thin film resistor formed of an N-type semiconductor thin film overlapping the P-type thin film resistor with an insulating layer interposed therebetween, so that a change in resistance value when stress is applied is prevented. In a bleeder resistor circuit, a resistance value of one unit is regulated by a resistance value formed by a combination of the P-type thin film resistor and the N-type thin film resistor so that an accurate voltage dividing ratio can be maintained when stress is applied.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a thin film resistor; a bleeder resistance circuit using a thin film resistor; and to a semiconductor device having the bleeder resistance circuit. 
     2. Description of the Related Art 
     Conventionally, a resistor made from a semiconductor thin film such as polysilicon and a bleeder resistance circuit using the resistor are used in many cases, and a resistor and a bleeder resistance circuit, which are formed using a semiconductor thin film having a conductivity type of either an N-type or a P-type, have been known. 
     However, when stress is applied to the conventional thin film resistor, for example, when resin packaging is made, there is a problem in that a resistance value of the thin film resistor is varied. Also, in the case of the bleeder resistance circuit, there is a problem in that a voltage dividing ratio is often varied after the resin packaging. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above, and an object of the present invention is therefore to provide a bleeder resistance circuit with high precision, in which an initial resistance value is kept after packaging and an accurate voltage dividing ratio can be kept in the case of the bleeder resistance circuit, and a semiconductor device with high precision using such a bleeder resistance circuit, for example, a semiconductor device such as a voltage detector or a voltage regulator. 
     To achieve the above object, means adopted in a semiconductor device of the present invention are as follows. A thin film resistor and a thin film resistor of a bleeder resistance circuit having a plurality of such thin film resistors are comprised of a P-type thin film resistor formed of an N-type semiconductor thin film. Also, the present invention is characterized in that a resistance value which is one unit in the bleeder resistance circuit is defined by a resistance value obtained by a combination of the P-type thin film resistor and the N-type thin film resistor and thus variations in resistance values of the P-type thin film resistor and the N-type thin film resistor by a piezo effect, which are described below, are cancelled by each other. Further, the present invention is characterized in that the P-type thin film resistor and the N-type thin film resistor are laminated in a vertical direction and thus an occupying area of the bleeder resistance circuit is reduced. 
     Hereinafter, variations in resistance values by the piezo effect and an influence on the bleeder resistance circuit will be described. 
     When the stress is applied to the thin film resistor, the resistance value of the thin film resistor is varied by a so-called piezo effect, and the resistance value of the P-type thin film resistor is varied in the direction opposite to a variation in the resistance value of the N-type thin film resistor. This is also confirmed by experiments of the present inventor(s). For example, the resistance value of the P-type thin film resistor is decreased and the resistance value of the N-type thin film resistor is increased. The direction of the variation is changed depending on the direction of the stress. 
     When the IC is packaged by a resin, the stress is produced. Thus, as described above, the resistance value of the thin film resistor is varied by the piezo effect. Although the bleeder resistance circuit is used for obtaining an accurate voltage dividing ratio, since the resistance values of the respective resistors are varied, the voltage dividing ratio is also varied. 
     The thin film resistor according to the present invention is composed of the P-type thin film resistor made from the P-type semiconductor thin film and the N-type thin film resistor made from the N-type semiconductor thin film. Thus, even if the stress is applied, a variation in the resistance value can be prevented. Also, a resistance value which is one unit in the bleeder resistance circuit is defined by a resistance value obtained by a combination of the P-type thin film resistor and the N-type thin film resistor. Therefore, even if the stress is applied, variations in the resistance values of the respective resistors are cancelled and thus an accurate voltage dividing ratio can be kept. Further, the P-type thin film resistor and the N-type thin film resistor are laminated in a vertical direction, and thus an occupying area of the bleeder resistance circuit can be reduced. 
     The thin film resistor of the semiconductor device according to the present invention is composed of the P-type thin film resistor made from the P-type semiconductor thin film and the N-type thin film resistor made from the N-type semiconductor thin film. Therefore, even if the stress is applied by resin packaging or the like, variations in the resistance values of the respective resistors are cancelled and thus an initial resistance value can be kept. Also, a resistance value which is one unit in the bleeder resistance circuit is defined by a resistance value obtained by a combination of the P-type thin film resistor and the N-type thin film resistor. Thus, an accurate voltage dividing ratio can be kept. When such a bleeder resistance circuit is used, a semiconductor device with high precision, for example, a semiconductor device such as a voltage detector or a voltage regulator can be obtained. Further, the P-type thin film resistor and the N-type thin film resistor are laminated in a vertical direction, and thus an occupying area of the bleeder resistance circuit can be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a schematic cross sectional view showing a semiconductor thin film resistor in a semiconductor device according to a first embodiment of the present invention; 
     FIG. 2 is a schematic cross sectional view showing a semiconductor thin film resistor in a semiconductor device according to a second embodiment of the present invention; 
     FIG. 3 is a block diagram of one embodiment of a voltage detector using a bleeder resistance circuit according to the present invention; and 
     FIG. 4 is a block diagram of one embodiment of a voltage regulator using a bleeder resistance circuit according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. 
     FIG. 1 is a schematic cross sectional view showing a semiconductor thin film resistor in a semiconductor device according to a first embodiment of the present invention. 
     A first insulating film  102  is formed on a semiconductor substrate  101 . A P-type polysilicon resistor  703  and an N-type polysilicon resistor  706  are formed on the first insulating film  102 . The P-type polysilicon resistor  703  has a P-type high resistance region  702  sandwiched between P-type low resistance regions  701  including heavy P-type impurities for making electrical connection with wiring patterns  802 . The N-type polysilicon resistor  706  has an N-type high resistance region  705  sandwiched between N-type low resistance regions  704  including heavy N-type impurities for making electrical connection with wiring patterns  802 . The wiring patterns  802  made of aluminum are connected with the P-type low resistance regions  701  and the N-type low resistance regions  704 . Here, even if stress is applied by resin packaging or the like, a variation in a resistance value of the P-type polysilicon resistor  703  and a variation in a resistance value of the N-type polysilicon resistor  706  can be cancelled by each other. Thus, a resistance value of a resistor  707  obtained by a combination of the P-type polysilicon resistor  703  and the N-type polysilicon resistor  706  can be kept to an initial resistance value. 
     In FIG. 1, the example of a combination of one P-type polysilicon resistor  703  and one N-type polysilicon resistor  706  is shown. However, the resistor  707  may be formed by a combination of a plurality of the P-type polysilicon resistors  703  and a plurality of the N-type polysilicon resistors  706 . 
     FIG. 2 is a schematic cross sectional view showing a semiconductor thin film resistor in a semiconductor device according to a second embodiment of the present invention. 
     The first insulating film  102  is formed on the semiconductor substrate  101 . A P-type polysilicon resistor  703  having a P-type high resistance region  702  sandwiched between P-type low resistance regions  701  including heavy P-type impurities for making electrical connection with wirings  802  is formed on the first insulating film  102 . Further, an N-type polysilicon resistor  706  having an N-type high resistance region  705  sandwiched between N-type low resistance regions  704  including heavy N-type impurities for making electrical connection with wirings  802  is formed on the P-type polysilicon resistor  703  through a second insulating film  801 . Here, one of the P-type low resistance regions  701  and one of the N-type low resistance regions  704  are connected with each other through the wiring  802  made of aluminum in the same contact hole  804 . The wiring  802  made of aluminum is extended onto the N-type polysilicon resistor  706 . Since the P-type polysilicon resistor  703  and the N-type polysilicon resistor  706  are laminated in a vertical direction, an occupying area of the bleeder resistance circuit in an IC chip can be reduced. 
     In FIG. 2, the example of a lamination of one P-type polysilicon resistor  703  and one N-type polysilicon resistor  706  is shown. However, the resistor  707  may be formed by a lamination of a plurality of the P-type polysilicon resistors  703  and a plurality of the N-type polysilicon resistors  706 . Also, in the example shown in FIG. 2, the N-type polysilicon resistor  706  is formed on the P-type polysilicon resistor  703 . However, the P-type polysilicon resistor  703  may be formed on the N-type polysilicon resistor  706 . 
     The resistor  707  obtained by a combination of the P-type polysilicon resistor  703  and the N-type polysilicon resistor  706 , as shown in FIGS. 1 and 2, is defined as one unit of the bleeder resistance circuit. Then, a plurality of resistors  707  is formed to construct the entire bleeder resistance circuit. In this manner, even if stress is applied by resin packaging or the like, an accurate voltage dividing ratio can be kept. When such a bleeder resistance circuit is used, a semiconductor device with high precision, for example, a semiconductor device such as a voltage detector or a voltage regulator can be obtained. 
     FIG. 3 is a block diagram of one embodiment of a voltage detector using a bleeder resistance circuit according to the present invention. 
     For the purpose of simplification, an example of a simple circuit is shown. However, in the case of an actual product, the other functions may be added if necessary. 
     Basic circuit structure elements of the voltage detector are a current source  903 , a reference voltage circuit  901 , a bleeder resistance circuit  902 , and a differential amplifier  904 . Further, an inverter  906 , N-type transistors  905  and  908 , a P-type transistor  907  and the like are added. Hereinafter, a part of the operation will be simply described. 
     When a voltage VDD is a predetermined reset voltage or higher, the N-type transistors  905  and  908  are turned OFF and the P-type transistor  907  is turned ON. Thus, the voltage VDD is output to the output terminal OUT. 
     At this point, the input voltage to the differential amplifier  904  becomes (RB+RC)/(RA+RB+RC)×VDD. 
     When the voltage VDD decreases and becomes a detection voltage or lower, a voltage VSS is output to the output terminal OUT. At this point, the N-type transistor  905  is turned ON and the input voltage to the differential amplifier  904  becomes RB/(RA+RB)×VDD. 
     As described above, the basic operation is performed such that the reference voltage generated in the reference voltage circuit  901  is compared with the voltage divided by the bleeder resistance circuit  902  in the differential amplifier  904 . Thus, the precision of the voltage divided by the bleeder resistance circuit  902  is very important. If the voltage dividing precision of the bleeder resistance circuit  902  is low, the input voltage to the differential amplifier  904  is varied and the predetermined reset voltage or the predetermined detection voltage is not obtained. When the bleeder resistance circuit according to the present invention is used, the voltage dividing with high precision after an IC is packaged by resin is allowed. Thus, a yield of the product as the IC can be improved and the voltage detector with higher precision can be manufactured. 
     FIG. 4 is a block diagram of one embodiment of a voltage regulator using the bleeder resistance circuit according to the present invention. 
     For the purpose of simplification, an example of a simple circuit is shown. However, in the case of an actual product, the other functions may be added if necessary. 
     Basic circuit structure elements of the voltage regulator are a current source  903 , a reference voltage circuit  901 , a bleeder resistance circuit  902 , a differential amplifier  904 , a P-type transistor  910  which acts as a current controlled transistor, and the like. Hereinafter, a part of the operation will be simply described. 
     The differential amplifier  904  compares the voltage divided by the bleeder resistance circuit  902  with the reference voltage generated in the reference voltage circuit  901 , and then supplies, to the P-type transistor  910 , a gate voltage required for obtaining a constant output voltage VOUT which is not influenced by changes in an input voltage VIN and a temperature. In the voltage regulator, as in the case of the voltage detector described in FIG. 3, the basic operation is performed such that the reference voltage generated in the reference voltage circuit  901  is compared with the voltage divided by the bleeder resistance circuit  902  in the differential amplifier  904 . Thus, the precision of the voltage divided by the bleeder resistance circuit  902  is very important. If the voltage dividing precision of the bleeder resistance circuit  902  is low, the input voltage to the differential amplifier  904  is varied and the predetermined output voltage VOUT is not obtained. When the bleeder resistance circuit according to the present invention is used, the voltage dividing with high precision after an IC is packaged by resin is allowed. Thus, the yield of the product as the IC can be improved and the voltage regulator with higher precision can be manufactured. 
     As described above, the thin film resistor of the semiconductor device according to the present invention is composed of the P-type thin film resistor made from the P-type semiconductor thin film and the N-type thin film resistor made from the N-type semiconductor thin film. Therefore, even if stress is applied by resin packaging or the like, variations in resistance values of respective resistors are cancelled and thus an initial resistance value can be kept. Also, in the bleeder resistance circuit, a resistance value as one unit is defined by a resistance value obtained by a combination of the P-type thin film resistor and the N-type thin film resistor. Thus, an accurate voltage dividing ratio can be kept. Further, since the P-type thin film resistor and the N-type thin film resistor are laminated, an area of the bleeder resistance circuit can be reduced. When such a bleeder resistance circuit is used, there is an effect that a semiconductor device with high precision, for example, a semiconductor device such as a voltage detector or a voltage regulator can be obtained with a small chip size.