SEMICONDUCTOR MEMORY DEVICE

Abstract: A semiconductor memory device including at least one pair of memory cell arays having (1, 2) a plurality of word lines (W+ 101, 102, ...), a plurality of bit lines (BL-1, BL-1 , BL-2, ...) and a plurality of memory cells (MC) disposed at the intersecting points of the word lines and the bit lines. A plurality of word line driving transistors (T(1), T(11)) are con­ nected to the word lines and aligned at the inner edges of the pair of memory cell arrays. The pitch of a pair of word line driving gate circuits (D01, D02; D11, D12) is matched to the pitch of the two adjacent wordlines, and at least a pair of word lines driving gate circuits are arranged along the direction of the word lines between the pair of memory cell arrays. The outputs of the word line driving gate circuits are connected to the word line driving transistors at both sides of the word line driving gate circuits. A plurality of decoder lines (D1, D2, D3, D4) extend between the pair of word line driving gate circuits (D01, D11) and are connected to the input terminals of the word line driving gate circuits.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern layout of a semiconductor memory device, more particularly to a pattern layout of word line driving gate circuits. 2. Description of the Related Art Large computers and supercomputers offer, increasingly sophisticated computation functions. Along with this, computers have become increasingly large in size. This has led to demands for miniaturization of computers. Large-scale computers and supercomputers must operate at a very high speed in order to perform massive computations in a short time period. Needless to say, bipolar circuits are used for the logic circuits. Bipolar memories, which can carry out read and write operations at a very high speed, are mainly used for the memory circuits. A tremendously large number of these bipolar memories are used in a computer. Therefore, to cope with demands for miniaturization of computers, it is strongly demanded that bipolar memories be developed which are more highly integrated and smaller in size. A bipolar memory is mainly composed of a memory cell having a flip-flop construction, X-decoder, Y-decoder, word line driver circuits, write/read circuits, and the like. In the prior art, the word line driving gate circuits for driving the word lines have usually been arranged at the ends of the word lines. This is because the patterns of prior art memory cells have been nearly equal in size to one of the transistors constituting the word line driving gate circuits and arrangement in a line of transistors constituting the word line driving gate circuits within a block enables the width of the patterns of the driver circuits to be made nearly equal to that of the memory cells. This has been a very rational and appropriate pattern layout. In such bipolar memories, however, the memory cells have been made increasingly denser and integrated due to the miniaturization of the transistors constituting the same. On the other hand, the word line driving gate circuits have to use transistors having a large current capacity just as in the past. This is because: (1) Cells in a bipolar memory are driven by current flowing from the word lines to the cells; (2) It is desirable to drive cells with a large current to speed up the operation of the cells; and (3) Even if cells are miniaturized and the driving current per cell decreased, the number of cells connected to a word line would be increased so as to attain the highest integration possible, resulting in the same driving current per word line. As a result, the pattern dimensions of the word line driving gate circuit cannot be reduced. Accordingly, in the prior art pattern layout, the word line driving gate circuits obstruct attempts to achieve a higher density, greater integrated memory, through miniaturization at memory cells. They result in wasted space between word lines. Moreover, it is desirable to make effective use of the space produced by thick power supply conductors for placement of decoders. SUMMARY OF THE INVENTION It is the main object of the present invention to provide an improved pattern layout of word line driving gate circuits in a semiconductor memory device. It is another object of the present invention to provide a technique for disposition of decoders in the space produced by thick power supply conductors for more effective design of a semiconductor memory device. The invention is specified in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further clarified by way of examples and with reference to the accompanying drawings, in which: Fig. 1 is a plan view of a prior art semiconductor memory device with word line driving gate circuits; Fig. 2 is a plan view of a semiconductor memory device with word line driving gate circuits in accordance with an embodiment of the present invention; Fig. 3 is a circuit diagram of an example of a word line driving gate circuit in the device of Fig. 2; Fig. 4 is a circuit diagram of an example of a memory cell in the device of Fig. 2; and Fig. 5 is a plan view for explaining the structure of the device of Fig. 2. DESCRIPTION OF THE PREFERRED EMBODIMENTS Before discussing the preferred embodiments, a look will be taken at the prior art pattern layout of word line driving gate circuits for reference. In Fig. 1, showing such a pattern layout, word lines WL-1, WL2, WL-3, ... are connected with memory cells (11, 12), (21, 22), (31, 32), ... with word line driving gate circuits WD-1, WD-2, WD-3, ... through transistors TR₁₂ , TR₂₂ , TR₃₂ , and with memory cells 13, 23, 33, ... through transistors TR₁₃ , TR₂₃ , TR₃₃ , The other pairs of terminals of the word line driving gate circuits WD-1, WD-2, ... are connected to the decoder lines. As can be seen, even if the memory cells are miniaturized, the word line driving gate circuits remain as they are, resulting in wasted dead spaces DS-1, DS-2, DS-3 DS-4, ... between word lines, that is, between WL-1 and WL-2, WL-2 and WL-3, WL-3 and WL-4, Further, on the extension of the word driving signal lines WL-11, WL-21, WL-31, WL-41, ... there are dead spaces DS-11, DS-21, DS-31, DS-41, According to the present invention, each two adjacent word lines are considered a pair. This ensures a dead space with a width of two memory cells connected with each adjacent word line, i.e., a width equivalent to the distance between two adjacent word lines. In that space, two word line driving gate circuit patterns of the same current capacity as the prior art, for driving the respective word lines are disposed along the direction of extension of the word lines. Further, decoder lines intersecting at right angles the word lines connected with the word line driving gate circuits are arranged in the pattern layout regions of word line driving gate circuits. This enables a high density of word lines in the region where the memory cells are arranged, that is, in the cell array region. Figure 2 is a plan view of pattern layout of word line driving gate circuits in a bipolar memory according to an embodiment of the present invention. In this and later figures, elements equivalent to those in prior figures bear identical reference numerals. In Fig. 2, 1 is an X address buffer circuit, 2 a Y-decoder circuit, and 4 a write/read circuit. D1 to Dn denote decoder lines, and WD₁ , WD₁₁ , WD₂ , WD₁₂ , ... WD n , WD ₁n are pairs of word line driving gate circuits, each including several driving transistors. The circuit diagram of a word line driving gate circuit is shown in Fig. 3. An example of the circuit of a memory cell is shown in Fig. 4. In Fig. 4, MC denotes a memory cell. W⁺ denotes a word line, W⁻ a hold line, BL and BL bit lines. In Fig. 2, V EE denotes an power supply voltage line e.g. -5.2 Volts, and V CC power supply voltage line or the ground line. In Fig. 2, decoder lines D1 to Dn originate from the X-address buffer circuit 1. Some decoder lines pass through the location of pairs of word line driving gate circuits. The Y-decoder circuit 2 is connected to the write/read circuit 4 by pairs of bit lines BL and BL , crossing word lines W⁺ and hold lines W⁻. Pairs of word lines W⁺ run at both sides decoder lines D1 to Dn at a different level and connect to the word line driving gate circuits. That is, a first word line W⁺ is connected to a word line driving gate circuit WD₁+DR₁ and a second word line W⁺ is connected to a word line driving gate circuit WD₁₁+DR₁₁. Similarly, a third word line is connected with a word line driving gate circuit WD₂+DR₂ , a fourth word line with a word line driving gate circuit WD₁₂+DR₁₂ , and so on. Note that these word line driving gate circuits include the word line driving transistors which will be explained later. On the other hand, a pair of power supply conductors V CC and V EE are provided on the integrated circuit containing the word lines W⁺, word line driving gate circuits (WD₁+DR₁ , WD₁₁+DR₁₁), (WD₂+DR₂ , WD₁₂+DR₁₂), and (WD n +DR n , WD₁ n +DR₁ n), and memory cells MC. Some of the power supply conductors V CC and V EE are arranged in parallel with the decoder lines D₁ to D n . The direction of the power supply conductors is perpendicular to the direction of the word lines W⁺. Moreover, a plurality of memory cells MC1(1), MC1(2), MC2(1), MC2(2), MC3(1), MC3(2), MC4(1), MC4(2), and so on are connected to word lines W⁺ and hold lines W⁻. For instance, memory cells MC1(1) and MC1(2) are connected with a word line 101 at one terminal and connected with a hold line 201 at the other terminal; a pair of memory cells MC2(1) and MC2(2) are connected with a hold line 202 at one terminal and with a word line 102 at the other terminal; and so on. Word lines 101, 102, 103, 104, ... and hold lines 201, 202, 203, 204, ... are arranged in parallel. Pairs of bit lines BL and BL are arranged perpendicular thereto. As is apparent from the above-described embodiment, there is provided a semiconductor memory device wherein groups of two word lines are connected as pairs. Only the region of pattern layout for the word line driving gate circuits spreads over a distance corresponding to two pairs of word lines. Two word line driving gate circuits are disposed in the region. Thus, the distance between word lines in the region of cell arrays can be kept small. That is to say, according to the structure of the present invention, two lines of memory cells are arranged at the side of one word line driving gate circuit. Figure 5 is a plan view for explaining the structure of the device of Fig. 2. In the figure at the both side of the decoder lines are shown a pair of memory cell arrays MC arrays-1 and -2 composed of plural memory cells, such as (MC1(1), MC1(2), MC2(1), and MC2(2)), (MC1(3), MC1(4), MC2(3), and MC2(4)), (MC3(1), MC3(2), MC4(1), and MC4(2)), and so on (MC1(4) and MC2(4) are not shown), word lines W⁺ 101, 102, 103, and 104, hold lines w⁻ 201, 202, 203, and 204, bit lines BL-1, BL-1 , BL-2, BL-2 , BL-3, BL-3 , and so on. There are pairs of word line driving transistors T(1), T(11); T(2), T(12); T(3), T(13); and T(4), T(14). The driving transistors T(1) and T(11), T(2) and T(12), T(3) and T(13), and T(4) and T(14) are respectively connected together to the word line driving gate circuits D01 , D11 , ... . Transistor T(1) is connected to the output of a word line driving gate circuit D01 , word line 101, and memory cells MC1(1) and MC1(2). Just as transistor T(1) is connected to the word line 101, transistor T(2) is connected to a word lined 102, T(3) to a word line 103, and T(4) to a word line 104. The plurality of transistors T(1), T(2), 7(3), ... and T(11), T(12), T(13), ... are aligned at the inner edges of the memory cell arrays, respectively. A pair of word line driving gate circuits D01 and D11 are arranged for a pair of memory cell arrays MEMORY CELL ARRAY-1 and MEMORY CELL ARRAY-2. A plurality of decoder lines D1, D2, D3 and D4 are connected to an address buffer 1 and coupled to the input of each word line driving gate circuit D01, D11. The vertical length of the word line driving gate circuit corresponds to twice the distance between two adjacent word lines. The outputs of the word line driving gate circuits are connected to the word line driving transistors T(1), T(2), ... T(11), T(12), ... at the two sides of the word line driving gate circuits. The voltage source line V CC may be arranged between the decoder lines and the memory cell arrays MC ARRAY 1 and 2 utilizing the dead space between them in parallel with the V EE line. The reason why the layout shown in Fig. 5 can eliminate the dead spaces explained in the prior art Figure 1 is explained hereinafter. In order to select the memory cells, the word line driving transistors, e.g., T(1), T(11), charge up the word line connected to the selected memory cell. Therefore, usually the word line driving transistors T(1), T(11) ... are connected to a wider power supply line V CC which is arranged over or next to the word line driving transistors. Since pairs of memory cell arrays MC ARRAY-1 and MC ARRAY-2 are arranged in order to decrease the number of memory cells which are connected to the single word line, pairs of word line driving transistor arrays T(1), T(2), ... T(4) and T(11), T(12), ... T(14) should be arranged right next to the edge of the memory cell arrays ARRAY-1 and ARRAY-2. This means that the pair wider power supply lines V CC (1), V CC (2) are also arranged next to the edge of the memory cell arrays ARRAY 1, 2. Now look at Fig. 1, taking into consideration the above issues in which if pair of memory cell arrays ARRAY-1 and ARRAY-2 are arranged at the both sides of the decoder lines, pairs of vertical arrayS of word line driver transistors and pairs of wider power supply voltage conductor lines should be arranged at the sides of the pair of memory cell arrays respectively. In Fig. 1, since the word line driving gate circuits WD-1, 2 ... are arranged only one side of the decoder lines, the dead spaces DS-11, DS-21, DS-31, DS-41 under the wider power supply conductor line V CC LINE which is connected to the word line driver transistors TR13, 23, 33, 43 (such connections not shown in Fig. 1). Furthermore, as already explained before, the problem occurs wherein the pitch of the word line driving gate circuits cannot cope with the pitch of the word lines. Under consideration of the above two problems or issues, the present embodiment in Fig. 5 can eliminate the dead spaces and can provide the best arrangement of the circuits layout of the memory circuit. That is, the word line driving gate circuits D01, D02 and D11, D12 are arranged in two vertical arrays which are at both sides of the decoder lines, and under each of the pair of wider power supply voltage line conductors V CC (1) and V CC (2). Note that the word line driving gate circuits are actually formed on the semiconductor substrate with a first lower conductive layer, and the power supply conductor lines V CC (1) and V CC (2), V EE (1) and V EE (2) are actually formed by a second upper conductive layer which is formed over the first lower conductive layer. And also, note that each collector of the word line driving transistors T(1), (2) to (4), T(11), (12) to (14) is connected to the power suppply conductor lines V CC (1) and V CC (2), but not shown such connection in Fig. 5. And the wider lower power supply lines V EE (1) and V EE (2) are connected to the each word line driving gate circuits D01 to D12, but such a connection is not shown in Fig. 5. While the present invention has been explained above in reference to bipolar memories, it will be apparent that it can also be applied to MOS memories.

Claims: A semiconductor memory device comprising: a pair of memory cell arrays having a plurality of word lines, a plurality of bit lines, and a plurality of memory cells disposed at intersecting points of said word lines and said bit lines; characterised by a plurality of word line driving transistors (T(11), T(1), ...) connected to said word lines and aligned at the inner edges of said pair of memory cell arrays; a plurality of pairs of word line driving gate circuits (D11, D01) whereby the word line driving gate circuits of each pair of said word line driving gate circuits are arranged along the direction of said word lines and disposed in the space between the extensions of lower adjacent word lines (W⁺111, W⁺112), said pairs of word line driving gate circuits being arranged perpendicularly to said word lines between said pair of memory cell arrays, the pitch of said pairs of word line driving gate circuits being matched to the pitch of adjacent word lines (W⁺111, W⁺112), the respective outputs of a pair of said word line driving gate circuits (D11, D01) being connected to the respective word line driving transistors of adjacent word lines at both sides of said pair of word line driving gate circuits; and a plurality of decoder lines (D1, D2, ...,) extending between said pair of word line driving gate circuits (D11, D01) and connected to the input terminals of said word line driving gate circuits (D11, D01). A semiconductor memory device according to claim 1, wherein a power supply conductor (V CC ) is arranged along a column of said word line driving transistors and connected to said word line driving transistors.

Inventors: ITAKURA, TOHRU
Applicants: FUJITSU LIMITED
Application year: 1985
Main classification: G11C8
IPC codes: G11C8, H01L27, G11C5, G11C11