JPH0298167A - Semiconductor device - Google Patents

Abstract

PURPOSE:To reduce a parasitic capacity under wiring pads and to alleviate a decrease in an input impedance by forming the pads for inputting a signal externally to a semiconductor integrated circuit containing a positive phase amplifier on a semiconductor region isolated from a substrate through an insulating layer. CONSTITUTION:A P-type epitaxial layer 2 having a P-type isolated region 3 is formed on the P-type semiconductor substrate 1 of a semiconductor integrated circuit, external wiring pads 5 are formed on the layer 2 through an insulating layer 4, and connected to a positive phase amplifier 6 in an integrated circuit. The layer 2 in which the potential branch point of dividing resistors 7, 8 is isolated is connected between the output terminal of the amplifier 6 and the ground. A parasitic capacity 9 between the pad 5 and the layer 2 isolated from the substrate 1 by the region 3 under the pad 5 is reduced to the ratio of the difference between an input signal amplitude and a signal amplitude from the potential branch point fed back to the layer 2 under the pad 5 by the input signal amplitude, thereby reducing the input impedance of the amplifier 6.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor integrated circuit (hereinafter referred to as an IC) including a positive phase amplifier circuit (hereinafter referred to as an amplifier).

BACKGROUND OF THE INVENTION FIG. 2 shows a schematic perspective view of the main parts of an IC including a conventional amplifier. In FIG. 2, an external connection pad 25 for inputting a signal from the outside at tC is formed on a p-type substrate 21 and is placed on an n-type epitaxial layer 22 fixed at the highest DC potential among the operating voltages. It is made with an insulating layer 24 in between.

Problems to be Solved by the Invention In such a conventional configuration, each circuit inside the IC, for example, is The input impedance of the amplifier 28 shown in FIG.
G When viewed from the outside, it becomes small.

In order to alleviate this problem, FIG. 3 shows 4 Mm, which is conventionally used, and the n-type epitaxy cell layer 22 under the external connection pad 25 is separated from other regions by the p-type layer 23. The parasitic capacitance is determined by the capacitance 26 between the external connection pad 25 and the n-type epitaxial layer 22 and the n-type epitaxial layer ↑I
The capacitance 27 is connected to the capacitance 27 between the p-type substrate 21 and the p-type substrate 21. However, even with this configuration, the input signal still charges and discharges the parasitic capacitance 26 existing between the n-type epitaxial layer 22 fixed at a DC potential and the external connection pad 25, and the input impedance does not decrease. Inevitable.

The present invention solves the above problem, and provides a semiconductor device that can minimize the drop in input impedance by reducing the parasitic capacitance related to external connection pads with a simple configuration in an IC that includes an internal amplifier. The purpose is to provide

Means for Solving the Problems In order to solve the above-mentioned problems, the semiconductor device of the present invention has a connection pad for inputting a signal from the outside to a semiconductor integrated circuit including a positive-phase amplifier circuit on a semiconductor region separated from a substrate. A semiconductor region separated from the substrate under the connection is connected to a potential branch point intermediate the output end of the positive phase amplifier circuit and ground.

Effect With the above configuration, the parasitic capacitance between the connection pad and the substrate and isolated semiconductor region below it is reduced by the difference between the input signal amplitude and the signal amplitude fed back to the isolated semiconductor region under the connection pad. In addition, the parasitic capacitance between the separated semiconductor region and the substrate is charged and discharged by the feedback signal, so that it no longer contributes to the input impedance. , the current required for the input signal to charge and discharge the parasitic capacitance under the connection pad becomes smaller, and the drop in human power impedance can be significantly reduced.

Example An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is a schematic perspective view of the main parts of an IC including an amplifier according to an embodiment of the present invention. In FIG. 1, a p-type semiconductor substrate 1
An n-type epitaxial layer 2 containing a p-type isolation region 3 on top of the
is formed, and an external connection pad 5 is formed on it via an insulating layer 4, and a positive phase amplifier circuit (amplifier) inside the IC is formed.
6. A dividing resistor 7.8 is connected between the output end of the amplifier 6 and the ground, and a potential branch point of the dividing resistors 7 and 8 is connected to the separated n-type epitaxial layer 2. The parasitic capacitance 9 between the external connection pad 5 and the n-type epitaxial layer 2 which is separated from the p-type substrate 1 by the p-type valve M region 3 therebelow is determined by the input signal amplitude and the n-type epitaxial layer under the external connection pad 5. This effectively reduces the difference in signal amplitude from the potential branch fed back to layer 2 to the ratio of the input signal amplitude. Furthermore, the parasitic capacitance 10 between the separated n-type epitaxial layer M2 and the p-type substrate 1 is
will be charged and discharged by the feedback signal and will no longer be involved in the input impedance. Therefore, if the value of the dividing resistor 7°8 connected to the output terminal of the amplifier 6 is appropriately selected and the amplitude of the feedback signal is set to 90% of the input signal amplitude, the input capacitance seen from the outside will be 0. 7PF~0.15PF
was able to be reduced to

Effects of the Invention As described above, according to the present invention, a connection pad for inputting a signal from the outside to a semiconductor integrated circuit including a positive phase amplifier circuit is placed at a potential branch point between the layer width circuit output and the ground. By forming this connection pad on a semiconductor region separated from the substrate via an insulating layer, it is possible to effectively reduce the parasitic capacitance under the connection pad, significantly reducing input impedance. It is extremely useful industrially.

[Brief explanation of drawings]

FIG. 1 shows the outline g15 of a semiconductor device showing one embodiment of the present invention.
The 4/1 diagram, FIG. 2, and FIG. 3 are block diagrams of main parts of conventional semiconductor devices, respectively. DESCRIPTION OF SYMBOLS 1... P-type semiconductor substrate, 2... N-type epitaxial layer, 3... P-type isolation region, 4... Insulating layer, 5...
External connection pad, 6... Positive phase amplifier circuit, 7, 8...
1 resistance, 9.10...parasitic capacitance. Agent Yoshihiro Morimoto Figure t...-P line a half-kitoi 4-11 extraction 2-n Sugimu Yu (Simal layer 3...-P type W request type % type % 5.・-ta E sound p, rape 5 line ha 0 dd 6... right and wrong tank? Goods return S (a) two) z8...-divided resistor 9, /θ... love capacity figure 2 Figure 3

Claims (1)

[Claims] 1. A connection pad for inputting a signal from the outside to a semiconductor integrated circuit including a positive phase amplifier circuit is formed on a semiconductor region separated from the substrate via an insulating layer, and the connection pad is separated from the substrate below the connection pad. A semiconductor device comprising: a semiconductor region connected to a potential branch point between an output terminal of the positive phase amplifier circuit and ground;