Transistor array structure

Description

TECHNICAL FIELD

The present invention relates generally to array structures, and more particularly to an array structure that may improve transistor characteristic measurement accuracy.

BACKGROUND OF THE INVENTION

Process variations can cause component characteristics on a semiconductor device to greatly vary. Test structures may be constructed to test operating characteristics of devices such as insulated gate field effect transistors (IGFETs). However, as devices operate at lower voltages and currents, measurements may be distorted by leakage currents in current paths other than the desired path of the device under test (DUT).

In view of the above, it would be desirable to provide a way of reducing or eliminating leakage currents in a device, such as an IGFET being tested.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a semiconductor circuit according to a first embodiment.

FIG. 2 is a circuit schematic diagram of an array of transistors according to an embodiment.

FIG. 3 is a circuit schematic diagram of drain mux circuit according to an embodiment.

FIG. 4 is a circuit schematic diagram of gate mux circuit according to an embodiment.

FIG. 5 is a circuit schematic diagram of an array drain drive circuit according to an embodiment.

FIG. 6 is a circuit schematic diagram of an array of transistors according to an embodiment.

FIG. 7 is a table showing potentials in which various signals and power supplies may be set when testing current characteristics of transistors according to an embodiment.

FIG. 8 is a table illustrating simulation results.

FIG. 9 is a flow diagram of a method of testing transistor characteristics according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various embodiments of the present invention will now be described in detail with reference to a number of drawings. The embodiments show transistor array circuits and methods constructed with insulated gate field effect transistors (IGFETs), for example IGFETs of complementary conductivity types (n-channel and p-channel types). In particular, the embodiments may include implementations using IGFETs having substantially lower absolute value of threshold voltage V_T, e.g. about 0.4 volts for n-channel IGFETs and about −0.4 volts for p-channel IGFETs as compared to about 0.6 volts and −0.6 volts, respectively. Such low threshold voltage IGFETs may comprise DDC technology, as but one example. DDC transistors are particularly advantageous for the embodiments herein based on the ability to reliably set threshold voltage with substantially reduced variation compared with conventional planar CMOS transistors. DDC transistors are also amenable to be designed with reduced threshold voltage, based upon, among other device design attributes, there being a heavily doped region and structure below a substantially undoped channel. Further discussion regarding transistor structure and methods of implementation is provided in U.S. Pat. No. 8,273,617 entitled ELECTRONIC DEVICES AND SYSTEMS, AND METHODS FOR MAKING AND USING THE SAME, which disclosure is incorporated by reference herein in its entirety. Such low threshold voltage IGFETs may be based upon a different transistor design, such as a design that is not planar but three-dimensional. Such low threshold voltage IFGETs may be produced on bulk silicon or on a substrate that has an insulating layer embedded therein.

Referring now to FIG. 1, a semiconductor circuit according to a first embodiment is set forth in a block schematic diagram, and designated by the general reference character 100. Semiconductor circuit 100 can include arrays (110-0 to 110-7). Each array (110-0 to 110-7) has a corresponding column of gate mux (multiplexer) circuits (130-0 to 130-7), row of drain mux circuits (120-0 to 120-7), and array drain drive circuits (140-0 to 140-7).

Each row of drain mux circuits (120-0 to 120-7) may receive column factor signals (CF1(7:0) and CF2(3:0)) and corresponding bank select signal (BS0 to BS7). Each column of drain mux circuits (120-0 to 120-7) may also receive a respective drain drive signal (DDRV0 to DDRV7) and a drain current reduction signal DTRACK.

Each column of gate mux circuits (130-0 to 130-7) may receive row factor signals (RF1(7:0) and RF2(3:0)) and corresponding bank select signal (BS0 to BS7). Each row of gate mux circuits (130-0 to 130-7) may also receive a gate drive signal GDRV and a gate line low drive signal GTRACK.

Array drain drive circuit (140-0 to 140-7) may receive a global drain drive signal GDDRV and may provide a local drain drive signal (DDRV0 to DDRV7), respectively to respective row of drain mux circuits (120-0 to 120-7).

Semiconductor circuit 100 may include an address generator 190. Address generator 190 may receive a clock signal CLK and a reset signal RST and may provide column factor signals (CF1(7:0) and CF2(3:0)), row factors (RF1(7:0) and RF2(3:0)), and bank select signal (BS7:0). Address generator 190 may be a clocked counter.

Referring now to FIG. 2, a circuit schematic diagram of an array according to an embodiment is set forth and given the general reference character 200. Array 200 can include transistors (N(1,1) to N(32,27)) arranged in a 32×27 matrix. Each transistor (N(1,1) to N(32,27)) may include a source terminal connected to ground a potential VSS, a gate connected to a respective gate line (GL-1 to GL-32), and a drain connected to a respective drain line (DL-1 to DL-27). For instance, transistor N(3,25) may have a gate connected to gate line GL3 in common with transistors (N(3,1) to N(3,24) (not shown), N(3,26) and N(3,27)) and a drain connected to drain line DL25 in common with transistors (N(1,25), N(2,25), and N(4,25) (not shown) to N(32,25)). Likewise, each transistor (N(1,1) to N(32,27)) can have a drain commonly connected with the drains of 31 other transistors along the same column and gates connected with the gates of 26 other transistors along the same row.

Each drain line (DL-1 to DL-27) may be connected to a row of drain mux circuits 220-k and each gate line (GL-1 to GL-32) may be connected to a column of gate mux circuits 230-k, where k=0-7 and denotes the array (110-0 to 110-7) that a bank select signal (BS0-7) selects (FIG. 1).

Array 200 may have 27 different types of transistors (i.e. different sizes, implant dopings, geometries, etc.) in the gate line (GL-1 to GL-32) direction. In this way, characteristics for different transistor types can be tested in each array. By having 32 transistors in each column connected to each drain line (DL-1 to DL-27), characteristic variations for same transistor types may be tested. Such variations may be caused by process variations or close proximity affects, for instance.

Referring now to FIG. 3, a circuit schematic diagram of a drain mux circuit according to an embodiment is set forth and designated by the general reference character 300. In each drain mux circuit 220-k of FIG. 2, there can be one drain mux circuit 300 for each drain line (DL-1 to DL-27). For instance, in array 200 of FIG. 2, there may be 27 drain mux circuits 300 in row of drain mux circuits 220-k.

Drain mux circuit 300 may receive column factor signals (CF1(7:0) and CF2(3:0)) and bank select signal BSk, drain drive signal DDRVk, and drain current reduction signal DTRACK. It is understood that only one of the column factor signals (CF1(7:0) and one of the column factor signals (CF2(3:0)) may be used per drain mux circuit 300 in accordance with the proper address decoding.

Drain mux circuit 300 may include logic gates (G302 and G304) and pass gates (PG302 and PG304). Logic gate G302 can receive column factors signals (CF1(7:0) and CF2(3:0)), and bank select signal BSk as inputs and may provide a data line select complement signal DSELECTN-n as an output. Logic gate G302 may be a NAND logic gate. Logic gate G304 may receive data line select complement signal DSELECTN-n and may provide a data line select signal DSELECT-n. Logic gate G304 may be an inverter logic gate. Logic gates (G302 and G304) may include complementary conductive type IGFETs with the p-channel IGFETs receiving a body bias potential Vbp1 at a body terminal and n-channel IGFETs receiving a body bias potential Vbn1 at a body terminal. Logic gates (G302 and G304) may receive a power supply potential VDD1 and a ground potential VSS1.

Pass gate PG302 may receive drain current reduction signal DTRACK, data line select signal DSELECT-n, and data line select complement signal DSELECTN-n as inputs and may have an output coupled to a drain line DL-n. Pass gate PG302 can include transistors (P302 and N302). Transistor P302 may be p-channel IGFET and transistor N302 may be an n-channel IGFET N302. Transistor P302 may provide a controllable impedance path between source and drain terminals connected between drain current reduction signal DTRACK and data line DL-n. Transistor P302 may receive data line select signal DSELECT-n at a gate terminal and a body bias voltage Vbp1 at a body bias terminal. Transistor N302 may be connected in parallel with transistor P302 to provide a controllable impedance path between source and drain terminals connected between drain current reduction signal DTRACK and data line DL-n. Transistor N302 may receive data line select complement signal DSELECTN-n at a gate terminal and a body bias voltage Vbn1 at a body bias terminal.

Pass gate PG304 may receive local drain drive signal DDRVk, data line select signal DSELECT-n, and data line select complement signal DSELECTN-n as inputs and may have an output coupled to a drain line DL-n. Pass gate PG304 can include transistors (P304 and N304). Transistor P304 may be p-channel IGFET and transistor N304 may be an n-channel IGFET N304. Transistor P304 may provide a controllable impedance path between source and drain terminals connected between local drain drive signal DDRVk and data line DL-n. Transistor P304 may receive data line select complement signal DSELECTN-n at a gate terminal and a body bias voltage Vbp1 at a body bias terminal. Transistor N304 may be connected in parallel with transistor P304 to provide a controllable impedance path between source and drain terminals connected between local drain drive signal DDRVk and data line DL-n. Transistor N304 may receive data line select signal DSELECT-n at a gate terminal and a body bias voltage Vbn1 at a body bias terminal.

Referring now to FIG. 4, a gate mux circuit according to an embodiment is set forth and designated by the general reference character 400. In each gate mux circuit 230-k of FIG. 2, there can be one gate mux circuit 400 for each gate line (GL-1 to GL-32). For instance, in array 200 of FIG. 2, there may be 32 gate mux circuits 400.

Gate mux circuit 400 may receive row factor signals (RF1(7:0) and RF2(3:0)) and bank select signal BSk, gate drive signal GDRV, and gate line low drive signal GTRACK. It is understood that only one of the row factor signals (RF1(7:0) and one of the row factor signals (RF2(3:0)) may be used per gate mux circuit 400 in accordance with the proper address decoding.

Gate mux circuit 400 may include logic gates (G402 and G404) and pass gates (PG402 and PG404). Logic gate G402 can receive row factors signals (RF1(7:0) and RF2(3:0)), and bank select signal BSk as inputs and may provide a gate line select signal GSELECT-m as an output. Logic gate G402 may be a NAND logic gate. Logic gate G404 may receive gate line select signal GSELECT-m and may provide a gate line select complement signal GSELECTN-m. Logic gate G404 may be an inverter logic gate. Logic gates (G402 and G404) may include complementary conductive type IGFETs with the p-channel IGFETs receiving a body bias potential Vbp2 at a body terminal and n-channel IGFETs receiving a body bias potential Vbn2 at a body terminal. Logic gates (G402 and G404) may receive a power supply potential VDD2 and a ground potential VSS2.

Pass gate PG402 may receive gate line low drive signal GTRACK, gate line select signal GSELECT-m, and gate line select complement signal GSELECTN-m as inputs and may have an output coupled to a gate line GL-m. Pass gate PG402 can include transistors (P402 and N402). Transistor P402 may be p-channel IGFET and transistor N402 may be an n-channel IGFET. Transistor P402 may provide a controllable impedance path between source and drain terminals connected between gate line low drive signal GTRACK and gate line GL-m. Transistor P402 may receive gate line select signal GSELECT-m at a gate terminal and a body bias voltage Vbp2 at a body bias terminal. Transistor N402 may be connected in parallel with transistor P402 to provide a controllable impedance path between source and drain terminals connected between gate line low drive signal GTRACK and gate line GL-m. Transistor N402 may receive gate line select complement signal GSELECTN-m at a gate terminal and a body bias voltage Vbn2 at a body bias terminal.

Pass gate PG404 may receive gate drive signal GDRV, gate line select signal GSELECT-m, and gate line select complement signal GSELECTN-m as inputs and may have an output coupled to a gate line GL-m. Pass gate PG404 can include transistors (P404 and N404). Transistor P404 may be p-channel IGFET and transistor N404 may be an n-channel IGFET. Transistor P404 may provide a controllable impedance path between source and drain terminals connected between gate drive signal GDRV and gate line GL-m. Transistor P404 may receive gate line select complement signal GSELECTN-m at a gate terminal and a body bias voltage Vbp2 at a body bias terminal. Transistor N404 may be connected in parallel with transistor P404 to provide a controllable impedance path between source and drain terminals connected between gate drive signal GDRV and gate line GL-m. Transistor N404 may receive gate line select signal GSELECT-m at a gate terminal and a body bias voltage Vbn2 at a body bias terminal.

Referring now to FIG. 5, a circuit schematic diagram of an array drain drive circuit according to an embodiment is set forth and designated by the general reference character 500. Array drain drive circuit 500 may be used as array drain drive circuit (140-0 to 140-7) in semiconductor circuit 100 of FIG. 1.

Array drain drive circuit 500 may receive bank select signal BSk and global drain drive signal GDDRV as inputs and may have an output connected to provide local drain drive signal DDRVk. Array drain drive circuit 500 may include a logic gate G502 and a pass gate PG502.

Logic gate G502 may receive bank select signal BSk as an input and may provide an output. Logic gate G502 may be an inverter. Logic gate G502 may include complementary conductive type IGFETs with the p-channel IGFETs receiving a body bias potential Vbp1 at a body terminal and n-channel IGFETs receiving a body bias potential Vbn1 at a body terminal. Logic gate G502 may receive a power supply potential VDD1 and a ground potential VSS1.

Pass gate PG502 may receive bank select signal BSk, the output of inverter G502, and global drain drive signal GDDRV as inputs and may have an output coupled to provide local drain drive signal DDRVk. Pass gate PG502 can include transistors (P502 and N502). Transistor P502 may be p-channel IGFET and transistor N502 may be an n-channel IGFET. Transistor P502 may provide a controllable impedance path between source and drain terminals connected between global drain drive signal GDDRV and local drain drive signal DDRVk. Transistor P502 may receive the output of logic gate G502 at a gate terminal and a body bias voltage Vbp1 at a body bias terminal. Transistor N502 may be connected in parallel with transistor P502 to provide a controllable impedance path between source and drain terminals connected between between global drain drive signal GDDRV and local drain drive signal DDRVk. Transistor N502 may receive bank select signal BSk at a gate terminal and a body bias voltage Vbn1 at a body bias terminal.

The operation of semiconductor circuit 100 of FIG. 1 will now be discussed with reference to FIGS. 1 to 5. In the example, bank 110-1 may be activated and transistor N(30,25) in array 200 of FIG. 2 will be selected.

Bank select signal BS1 may transition to a high logic level to activate bank 110-1. The predetermined set of two row factors (RF1(7:0) and RF2(3:0)) uniquely received by gate G402 of gate mux circuit 400 (each of the other gate mux circuits 400 in column of gate mux circuits 130-1, receive a different unique combination of two row factors (RF1(7:0) and RF2(3:0))) may be at a high logic level. In this way, logic gate G402 may provide a gate line select complement signal GSELECTN-m, in this case m=30, having a logic low level and logic gate G404 may provide a gate line select signal GSELECT-m having a logic high level. With gate line select signal GSELECT-m at a logic high level, pass gate PG402 may be turned off and pass gate PG404 may be turned on and a low impedance path may be provided between gate drive signal GDRV and gate line GL-m, where m=30. In this way gate line GL-30 may be driven by gate drive signal GDRV through pass gate PG404.

All the other gate mux circuits 400 in column of gate mux circuits 130-1 that drive gate lines (GL-1 to GL-29, GL-31, and GL32) provide a gate line select signal GSELECT-m at a logic low level. With gate line select signal GSELECT-m at a logic low level, pass gate PG402 may be turned on and pass gate PG404 may be turned off and a low impedance path may be provided between gate line low drive signal GTRACK and gate line GL-m, where m=1=29, 31 and 32). In this way gate lines (GL-1 to GL-29, GL-31, and GL32) may be driven by gate line low drive signal GTRACK through pass gate PG402.

With bank select signal BS1 at a logic high level, pass gate PG502 in drive mux circuit 500 may be turned on and a low impedance path may be provided between global drain drive signal GDDRV and local drain drive signal DDRV1.

The predetermined set of two column factors (CF1(7:0) and CF2(3:0)) uniquely received by gate G302 of drain mux circuit 300 (each of the other drain mux circuits 300 in row of column mux circuits 120-1, receive a different unique combination of two column factors (CF1(7:0) and CF2(3:0))) may be at a high logic level. In this way, logic gate G302 may provide a drain line select complement signal DSELECTN-n, in this case m=25, having a logic low level and logic gate G304 may provide a drain line select signal DSELECT-n having a logic high level. With drain line select signal DSELECT-n at a logic high level, pass gate PG302 may be turned off and pass gate PG304 may be turned on and a low impedance path may be provided between local drain drive signal DDRV1 and drain line DL-n, where n=25. In this way gate line DL-25 may be driven by global drain drive signal GDDRV through pass gates PG502 and PG304.

All the other drain mux circuits 300 in row of drain mux circuits 120-1 that drive drain lines (DL-1 to DL-24, DL-26, and DL27) provide a drain line select signal DSELECT-n at a logic low level. With drain line select signal DSELECT-n at a logic low level, pass gate PG302 may be turned on and pass gate PG304 may be turned off and a low impedance path may be provided drain current reduction signal DTRACK and gate line DL-n, where n=1-24, 26, and 27). In this way drain lines (DL-1 to DL-24, DL-26, and DL27) may be driven by drain current reduction signal DTRACK through pass gate PG302.

As described above, the column of drain mux circuits 120-k may operate to drive a selected drain line DL-25 with a global drain drive signal GDDRV by way of pass gates (PG502 and PG304) while driving unselected drain lines (DL-1 to DL-24, DL-26, and DL27) with a drain current reduction signal DTRACK through pass gate PG302. In this way, a potential drop across the unselected pass gates PG304 (e.g. the 26 unselected pass gates PG304) connected to local drain drive signal DDRVk may be reduced to zero thereby eliminating or significantly reducing channel leakage currents to unselected columns. By reducing the potential across the unselected pass gates, a drive current through drain drive signal GDDRV may more accurately represent the actual drain current in selected transistor N(30,25). In this way, testing characteristics of a selected transistor N(30,25) can be more accurately performed.

For transistors operating with extremely low currents, for example low voltage IGFETs, such as FINFETs, DDC transistors, and/or transistors operating in subthreshold regions, the reduction of alternate leakage current paths may be particularly necessary to provide accurate current measurements.

In yet another feature, the row of gate mux circuits 130-k may operate to drive a selected gate line GL-30 with a gate drive signal GDRV by way of pass gate PG404 while driving unselected gate lines (GL-1 to GL-29, GL-31, and DL-32) with a gate line low drive signal GTRACK through pass gate PG402. In this way, a gate potential of unselected transistors (e.g. the 31 unselected transistors (N(1,25) to N(29,25), N(31,25), and N(32,25) along drain line DL25) may be set to a potential below ground potential VSS. The low gate potential may provide a substantially higher impedance path through the unselected transistors (N(1,25) to N(29,25), N(31,25), and N(32,25) along drain line DL25) and leakage current along drain line DL-25 may be substantially reduced. In this way, testing characteristics of a selected transistor N(30,25) can be more accurately performed.

Referring now to FIG. 6, a circuit schematic diagram of an array according to an embodiment is set forth and given the general reference character 600.

Array 600 of FIG. 6 may differ from array 200 of FIG. 2 in that transistors (N(1,1) to N(32,27)) can be p-channel IGFETs. In this configuration, the common sources of the transistors (N(1,1) to N(32,27)) may be connected to a power supply potential VDDSOURCE. Note that with back bias potentials (Vbn1 and Vbn2) normally separated between the column and row paths, in the embodiment tying the two voltages together improves the test accuracy for drain current IDD and gate voltages VG.

Referring now to FIG. 7, a table is set forth and designated by the general reference character 700. Table 700 may include potentials in which various signals and supplies may be set when testing current characteristics of transistors in an n-channel array 200 and a p-channel array 600.

Referring now to FIG. 8, a table is set forth and designated by the general reference character 800. Table 800 sets forth simulation results of drain current IDD actually flowing through the transistor in the array being tested as well as the drain current IDD flowing from an output pad that may drive the global drain drive signal GDDRV as well as the actual gate potential on the transistor in the array being tested as well as the potential placed on the pad connected to gate drive signal GDRV. As can be seen, the actual current IDD is about the same as the current flowing from the output pad, with essentially matching actual gate line (GL-m) potential and gate drive signal GDRV potential indicating that the methods described above are substantially reducing leakage current that can otherwise make test results inaccurate.

Referring now to FIG. 9, a flow diagram according to an embodiment is set forth and given the general reference character 900. Flow diagram 900 illustrates testing semiconductor circuit 100 of FIG. 1. Flow diagram 900 will now be described with reference to FIG. 9 in conjunction with FIGS. 1 and 2.

At step S910, the semiconductor circuit 100 may be provided on a probing apparatus. At step S920, a reset signal RST may be provided. In this way, address generator 190 may be reset to begin incrementing at the first address. At step S930, gate drive signal GDRV may be provided on a pad. At step S940, gate line low drive signal GTRACK may be provided on a pad. At step S950, global drain drive signal GDDRV may be provided on a pad. At step S960, drain current reduction signal DTRACK may be provided on a pad. At this point, the gate drive signal GDRV can be provided to the gate terminal of the transistor being tested, for instance, GL1 connected to transistor under test N(1,1). Global drain drive signal GDDRV may be provided to the drain line of the transistor being tested, for instance DL1 connected to transistor under test N(1,1). Also, at this time, the gate line low drive signal GTRACK can be provided to the gate lines (GL2-GL32) of transistors that are not selected and the drain current reduction signal can be provided to the drain lines (DL2-DL27) of transistors that are not selected. At step S970, the current flowing through global drain drive signal GDDRV may be determined. The current in step S970 may have a current value that is essentially the same as the current flowing through the transistor under test N(1,1). By driving a target current through drive signal at given drain voltage and slewing gate voltage, the gate voltage rises until the target current is hit, then the gate voltage can be measured for a selected drain voltage (typically value of 0.1V or Vdd).

At step S980, the clock signal CLK may transition through one clock cycle. In this way, address generator may output a subsequent address. The process may return to step S930 to test a subsequent transistor in accordance with the subsequent address. The test process may continue in this manner until all of the transistors in all of the arrays (110-0 to 110-7) may be tested.

The appearance of the phrase “in one embodiment” in various places in the specification do not necessarily refer to the same embodiment. The term “to couple” or “electrically connect” as used herein may include both to directly and to indirectly connect through one or more intervening components. While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. Accordingly, the specifications and drawings are to be regarded in an illustrative rather than a restrictive sense.