JP2881894B2 - Resistor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistor formed in a semiconductor integrated circuit device or the like.

[Summary of the Invention]

The present invention reduces the temperature dependence of the resistance value by connecting an n-channel thin film transistor and a p-channel thin film transistor, each of which has a temperature-dependent current characteristic opposite to each other, to form a resistor. It was done.

[Prior Art] A resistor in a semiconductor integrated circuit device or the like is generally made of
It is composed of a film, and may be composed of a MOS transistor or the like.

[Problems to be solved by the invention]

By the way, MOS-SRAM load resistors are MΩ
High resistance is required, and even for bipolar devices, kΩ
A high degree of resistance is often required.

On the other hand, since polycrystalline Si is a semiconductor, if the energy at the bottom of the conduction band is E _c and the Fermi level is E _f , the resistance R
It is expressed as _{R = R 0 exp {(E} c -E f) / kT}.

Therefore, in order to obtain a high resistance, it is necessary to increase E _c −E _f by positioning E _f near the center of the forbidden band. However, increasing the E _c -E _f, as is apparent from the above equation, the temperature dependence of the resistance value R becomes large. Therefore, in a polycrystalline Si film, it is theoretically difficult to form a resistor having a high resistance and a small temperature dependence of the resistance value, and a margin in design and operation is small.

Further, in the MOS transistor, whose transconductance g _m is proportional to the mobility mu, the mobility of the single crystal Si is greatly affected by scattering due to acoustic type lattice vibration. Therefore, as the temperature increases, the mobility and the transconductance decrease, and the resistance value increases. Although the characteristics are opposite to those of the polycrystalline Si film, the temperature dependence is also large.

[Means for solving the problem]

The resistor according to the present invention is formed by connecting an n-channel thin film transistor and a p-channel thin film transistor whose current-dependent temperature characteristics are opposite to each other.

[Action]

In the resistor according to the present invention, the temperature dependence of the current is offset by the n-channel thin film transistor and the p-channel thin film transistor.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

In this embodiment, an n-channel and p-channel thin film transistor having a dendritic polycrystalline Si film as an active layer is formed, and these thin film transistors are formed as shown in FIG. 1A or FIG.
They are connected as shown in Fig. 1B.

To form a dendritic polycrystalline Si film, a normal polycrystalline Si film is made amorphous by ion implantation of Si ⁺ , or an amorphous Si film is formed from the beginning at a low temperature, 60 crystalline Si films
Anneal at a low temperature of about 0 ° C. for solid phase growth.

Dendritic polycrystalline Si has a larger grain size and improved electrical properties of grain boundaries than ordinary polycrystalline Si, and therefore has fewer traps. For this reason, dendritic polycrystalline Si is
Has properties intermediate between that of ordinary polycrystalline Si.

By the way, as described above, the mobility of single-crystal Si is greatly affected by the scattering due to the acoustic lattice vibration. Therefore, the mobility decreases as the temperature increases.

On the other hand, since ordinary polycrystalline Si has many traps, its mobility is greatly affected by scattering by ionized impurities. Therefore, the mobility increases as the temperature increases.

However, as described above, dendritic polycrystalline Si has intermediate properties between single-crystal Si and ordinary polycrystalline Si, and thus the mobility itself has a small temperature dependence.

FIG. 2 shows an n-channel thin film transistor having a dendritic polycrystalline Si film as an active layer and a gate width and a gate length of 20 μm and 7 μm, respectively, and a gate width and a gate length of 40 μm and 7 μm, respectively. 9 shows temperature dependence of current with a certain p-channel thin film transistor.

As is apparent from FIG. 2, the characteristics of the n-channel thin film transistor when the ordinary polycrystalline Si film is used as the active layer remain slightly, and the characteristics of the p-channel thin film transistor when the single crystal Si substrate is used are slightly different. Although appearing, the current dependence itself is small.

Therefore, in the present embodiment shown in FIG. 1, the temperature dependence of the current is canceled out by the n-channel thin film transistor and the p-channel thin film transistor, and the temperature dependence of the entire resistance value is very small.

In addition, as the thickness of the dendritic polycrystalline Si film constituting the active layer of the thin film transistor is reduced, apparent traps per unit area are reduced, which is effective in reducing the temperature dependence of the resistance value. It is a target.

In order to adjust the resistance value of the resistor of the present embodiment as described above, for example, the gate length is kept constant and the gate width is varied.

In the case of bipolar devices, this process must be added because the manufacturing process of the thin film transistor is not included in the manufacturing process.However, when the manufacturing process of the thin film transistor is originally included, such as in a MOS-SRAM, the process is conventionally performed. You can be on the street.

〔The invention's effect〕

In the resistor according to the present invention, the temperature dependence of the current is canceled out by the n-channel thin film transistor and the p-channel thin film transistor, so that the temperature dependence of the resistance value is small.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a graph showing temperature-dependent characteristics of current of an n-channel and p-channel thin film transistor having a dendritic polycrystalline Si film as an active layer.

──────────────────────────────────────────────────続 き Continuing on the front page (51) Int.Cl. ⁶ identification code FI H01L 27/092 (58) Investigated field (Int.Cl. ⁶ , DB name) H01L 21/8234-21/8238 H01L 21/8249 H01L 27/04 H01L 27/06 H01L 27/088-27/092

Claims (1)

(57) [Claims] 1. A resistor formed by connecting an n-channel thin film transistor and a p-channel thin film transistor whose current-dependent temperature characteristics are opposite to each other.