Patent Publication Number: US-11657868-B2

Title: Multi-die memory device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. Ser. No. 17/135,112, filed Dec. 28, 2020, entitled MULTI-DIE MEMORY DEVICE, which is a Continuation of U.S. Ser. No. 16/823,122, filed Mar. 18, 2020, entitled MULTI-DIE MEMORY DEVICE, now U.S. Pat. No. 10,885,971, which is a Continuation of U.S. Ser. No. 16/211,966, filed Dec. 6, 2018, entitled MULTI-DIE MEMORY DEVICE, now U.S. Pat. No. 10,607,691, which is a Continuation of U.S. Ser. No. 15/809,925, filed Nov. 10, 2017, entitled MULTI-DIE MEMORY DEVICE, now U.S. Pat. No. 10,157,660, which is a Continuation of U.S. Ser. No. 15/098,269, filed Apr. 13, 2016, entitled MULTI-DIE MEMORY DEVICE, now U.S. Pat. No. 9,818,470, which is a Continuation of U.S. Ser. No. 14/797,057, filed Jul. 10, 2015, entitled MULTI-DIE MEMORY DEVICE, now U.S. Pat. No. 9,324,411, which is a Continuation of U.S. Ser. No. 14/278,655, filed May 15, 2014, entitled MULTI-DIE MEMORY DEVICE, now U.S. Pat. No. 9,082,463, which is a Continuation of U.S. Ser. No. 13/562,242, filed Jul. 30, 2012, entitled MULTI-DIE MEMORY DEVICE, now U.S. Pat. No. 8,737,106, which is a Continuation of U.S. Ser. No. 12/519,353, filed Jun. 15, 2009, entitled MULTI-DIE MEMORY DEVICE, issuing as U.S. Pat. No. 8,233,303 on Jul. 31, 2012, which claims priority under 35 U.S.C. § 365 to International Application No. PCT/US2007/087359, filed Dec. 13, 2007, published as WO 2008/076790 A2 on Jun. 26, 2008, which claims priority under 35 U.S. C. § 119(e) to U.S. Provisional Application No. 60/870,065, filed Dec. 14, 2006, entitled MULTI-DIE MEMORY DEVICE, all of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to data storage technology. 
     BACKGROUND 
     Power consumption in dynamic random access memory (DRAM) devices has historically scaled in proportion to the product of signaling bandwidth and storage capacity. As more applications demand higher performance and higher capacity, DRAM power consumption is projected to increase dramatically, presenting substantial cooling challenges for system designers and making advances in signaling rate and capacity increasingly difficult. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG.  1    illustrates an embodiment of an integrated circuit package having synchronous, high-speed interface and core storage functions split between an interface die and a storage die, respectively; 
         FIG.  2    illustrates an embodiment of an interface die that may be used to implement the interface die of  FIG.  1   ; 
         FIG.  3    illustrates a portion of a inverter-based clock distribution circuit implemented in a conventional DRAM process and a counterpart inverter-based clock distribution circuit implemented in a high-speed logic process; 
         FIG.  4    illustrates a comparison between a conventional arrangement of a storage array coupled to a centralized I/O and an arrangement that may be used within the storage die of  FIG.  1   ; 
         FIG.  5 A  illustrates an exemplary arrangement of storage arrays within a storage die and  FIG.  5 B  illustrates a more detailed embodiment of a representative storage array within the arrangement of  FIG.  5 A ; 
         FIGS.  6 A and  6 B  illustrate embodiments of multi-component packages having separate storage and interface dice; 
         FIG.  7 A  illustrates an embodiment of a multi-die memory device having an interface die that may be configured at run-time or production time to establish a selected interface data width and data rate; 
         FIG.  7 B  illustrates an exemplary serializing circuit that may be provided within an interface die to support configurable serialization of read data returned from a storage die within a multi-die memory device; 
         FIG.  8    illustrates an alternative embodiment of a multi-die memory device having multiple storage dice coupled to a shared interface die; 
         FIG.  9    illustrates an alternative embodiment of a multi-die memory device in which an interface die includes a dedicated set of data interfaces for each storage die; 
         FIG.  10    illustrates an embodiment of a multi-die memory device in which an interface die outputs a demand signal to a selected one of multiple storage dice to enable read-data output; 
         FIG.  11    illustrates an embodiment of a timing arrangement for bi-directional data transmission between the storage die and interface die of  FIG.  10   ; 
         FIG.  12    illustrates a more detailed embodiment of a multi-die memory device in which a demand signal is used to effect time-multiplexed read data transfer between an interface die and a storage die; 
         FIG.  13    illustrates an exemplary memory-read command sequence and corresponding read data transfer sequence within the multi-die memory device of  FIG.  12   ; 
         FIG.  14    illustrates an embodiment of a data transmit circuit that may be used to implement data transmitter of  FIG.  12   ; 
         FIG.  15    illustrates embodiments of a serializer and latch that may be used to implement the serializer and latch of  FIG.  14   ; 
         FIGS.  16 A and  16 B  illustrate an exemplary timing calibration operation that may be carried out by the interface die of  FIG.  12    to determine an appropriate time delay between assertion of the demand signal and assertion of the corresponding read data sampling signal; 
         FIG.  17 A  illustrates a multi-die memory device having an interface die that provides one or more supply voltages to output drivers within a counterpart storage die to control the amplitude of output signals generated by the storage die; 
         FIG.  17 B  illustrates amplitudes of exemplary output signals generated by the storage die of  FIG.  17 A  in response to different supply voltages from the counterpart interface die; 
         FIG.  18    illustrates a multi-die memory device having an interface die with built-in self-test circuitry and redundancy control circuitry; 
         FIG.  19    illustrates an embodiment of a multi-die memory device in which an interface die includes a power regulator to selectively power each of multiple storage arrays \ within a storage die; 
         FIG.  20 A  illustrates an exemplary packaging arrangement that may be used to encapsulate a pair of storage dice within a multi-die memory device; 
         FIG.  20 B  illustrates an exemplary packaging arrangement that may be used to encapsulate a generalized number of storage dice within a multi-die memory device; 
         FIG.  20 C  illustrates another packaging arrangement in which an interface die and storage die are packaged separately in packages that mate to one another to form a multi-package module; 
         FIG.  20 D  illustrates another packaging embodiment in which an interface die is mounted in a flip-chip orientation to a module substrate; 
         FIG.  20 E  illustrates a package-on-package embodiment having a storage package stacked on an interface package; 
         FIG.  20 F  illustrates another package-on-package embodiment having multiple storage packages stacked on an interface package; 
         FIG.  21    illustrates an embodiment of a memory module having rows of multi-die memory devices disposed on front and rear faces; 
         FIG.  22    illustrates a memory subsystem that includes a memory controller and a pair of multi-die memory devices disposed in a package-on-package arrangement; 
         FIG.  23    illustrates a high-level block diagram of a pulsed signaling multiplexer that may be used to perform serializing operations and other functions within a storage die and/or interface die within a multi-component package or other multi-chip package; 
         FIG.  24    illustrates a timing circuit that may be used in conjunction with the multiplexer of  FIG.  23   ; and 
         FIG.  25    illustrates a timing diagram for the multiplexer of  FIG.  23   . 
     
    
    
     DETAILED DESCRIPTION 
     A memory device having storage and control functions split between separate integrated circuit dice within a multi-die integrated circuit package is disclosed in various embodiments. In particular, recognizing that compromises inherent in conventional DRAM fabrication processes yield relatively inefficient high-speed logic circuitry, reduced power may be achieved by relegating the high-speed circuitry that forms the control and signaling interface of a conventional memory device to a separate interface die that is fabricated using a process that yields power-efficient high-speed circuitry. With most or all of the high-speed circuitry removed, the core storage circuitry that remains on the storage die may be fabricated in a process that is more appropriate to balancing cell retention time and storage density, potentially saving additional power. Also, by disposing the interface die and the storage die in close proximity to one another within a common integrated circuit (IC) package (e.g., a multi-component package (MCP) such as a stacked package die, also known as a multi-die package (MDP), multi-chip module (MCM), system-in-package (SIP), etc.), a substantially larger number of die-to-die interconnections may be achieved than if each of the dice is enclosed within separate IC packages. In particular, in one embodiment, the larger number of die-to-die interconnects possible within a multi-die package are applied to establish a dedicated set of control and data signal paths between the interface die and each of multiple storage arrays within the storage die. In one embodiment, the intra-package data signal interconnects are disposed at a central region within each of the storage arrays of the storage die thus enabling substantially shorter bit lines to be used than in arrangements having bit lines that traverse the entire storage array, thereby increasing data retrieval speed and/or significantly reducing access power at nominal speeds. 
     In one embodiment, the interface die and storage die are disposed in a stack (i.e., one on top of another) on top of a multi-die package substrate. The top die in the stack, which may be the interface die or the storage die, may be wire-bonded to conductive traces or other conductive structures in the package substrate to establish connection to the bottom die. The bottom die may also be wire bonded to the conductive structures within the package substrate or may be coupled to the conductive structures via flip-chip arrangement or any other interconnection arrangement. In another embodiment, the interface die and storage die may be mounted side-by-side on the package substrate, and may be directly wire bonded to one another and/or flip-chip-interconnected or wire-bond-interconnected through conductive structures in the package substrate. There are many other embodiments in which the interface die is interconnected to the storage die using a variety of “3D packaging” technologies including, but not limited to, thru-silicon vias, flex-tape, die-in-substrate encapsulation, direct wafer bonding, proximity interconnect, and so forth. In any of these variants, the MCP may include an encapsulating structure or other housing disposed over the interface die and storage die to form an integrated-circuit (IC) package. Further, the separate interface and storage dice may cooperate to mimic the functional operation of conventional memory devices and the multi-die memory package may be form-factor and contact-compatible with such memory devices. Accordingly, the multi-die memory device may be disposed in place of conventional memory devices on memory modules, motherboards, or in any other application where conventional memory devices may be applied. Further, additional storage dice may be included within the multi-die memory device, each coupled to the interface die but omitting full-time clocked input/output circuitry and thus multiplying storage capacity without substantially increasing static power consumption. These and other embodiments are described in further detail below. 
       FIG.  1    illustrates an embodiment of an IC package  100  having synchronous, high-speed interface and core storage functions split between an interface die  101  and a storage die  103 , respectively. The interface die  101 , also called an I/O and control die, includes a high-speed interface  107  and multiple internal memory array interfaces  105   1 - 105   4 . In the embodiment of  FIG.  1   , the high-speed interface  107  is a synchronous interface that receives timing signals and memory access commands from an external memory controller (not shown), and that receives write data in conjunction with memory write commands and outputs read data in response to memory read commands. In a particular embodiment, the high-speed interface  107  may be designed to mimic the interface of a conventional memory device and thus may receive commands (or requests) via a command path  108  (Cmd/Req) synchronously with respect to a clock signal received via a clock/chip-select path  109  (Clk/CS), and may receive data via a data path  110  (Data/Strobe) in response to transitions of corresponding strobe signals (i.e., timing references) conveyed source synchronously on strobe lines within the data path  110 . The high-speed interface  107  may additionally include timing circuitry such as a phase-locked loop (PLL) or delay-locked loop (DLL) circuitry to generate an internal clock signal based on a reference clock signal received via the clock path  109 . In one embodiment, for example, the internal clock signal is used to sample command signals conveyed via the command path  108 , and to generate strobe signals that are output via data path  110  in conjunction with read data, thereby providing a source-synchronous timing reference for establishing a read-data sampling time within the external memory controller. The timing circuitry within the high-speed interface  107  may additionally include phase adjustment circuitry to enable desired phase offsets between the internal clock signal and reference clock signal and/or between data signal sampling times and transitions in corresponding incoming data strobe signals. 
     In the embodiment of  FIG.  1   , each of the memory array interfaces  105   1 - 105   4  (DRC Q1 -DRC Q4 ) is coupled to a respective storage array  104   1 - 104   4  within the storage die  103 , and includes a relatively slow and wide data path (i.e., relative to the high-speed interface  107 ) that, in one embodiment, matches the column access width of the storage array, as well as an asynchronous command path for conveying row and column control signals to the storage array. That is, the command transfer from interface die  101  to storage die  103  is clockless (or un-clocked) in that no periodic clock signal is conveyed along with the row and column control signals, though one or more non-periodic strobe signals such as row-address-strobe (RAS) and column-address-strobe signals (CAS) may be issued to initiate address latching and corresponding memory access operations within the storage die. By minimizing the use of free-running or continuous clocking circuitry on the storage-die, and instead having the interface die provide a timing reference signal only when needed (e.g., during signal transmission between the storage die and the interface die) substantial power savings can be realized. A clocked command path (and corresponding clocked interface in the storage die) may be used for command transfer in alternative embodiments. The data signal transfer between the interface die  101  and storage die  103  may be timed by a clock or strobe signal, or may be transmitted asynchronously. In the case of asynchronous data transmission, sampling time within the interface die  101  and/or storage die  103  may be established deterministically with respect to transmission or receipt of row/column control signals. 
     In the embodiment of  FIG.  1   , the storage die  103  includes four independently accessible storage arrays  104   1 - 104   4  (Q1-Q4 and also referred to herein as quadrants, though more or fewer arrays may be provided in alternative embodiments), each coupled to a respective one of the memory array interfaces  105   1 - 105   4  within the interface die  101 . As discussed in further detail below, the separate signaling paths between the storage arrays  104  and the interface die  101  enable the storage arrays  104  to be designed with substantially shorter data bit lines than in conventional memory devices that have a single multiplexed I/O node. 
       FIG.  2    illustrates an embodiment of an interface die  125  that may be used to implement the interface die  101  of  FIG.  1   . As shown, interface die  125  includes I/O circuitry  126  that forms at least a portion of the high-speed interface  107  described above, and includes a command interface  127  to receive commands (or requests) from an external control device, a clock/chip-select interface  128  to receive a reference clock signal, clock-enable signal, chip-select signal and other timing and/or control-related signals (e.g., serial I/O signals that may be used to configure the operation of the high-speed external interface prior to normal device operation), and a data I/O interface  129  to receive write data signals and corresponding strobe signals and mask signals, and to output read data and corresponding strobe signals. The input/output circuitry  126  is coupled to a core logic block  130  that includes command decode circuitry  131  (referred to herein as a command decoder), timing circuitry  133  and data serializing and deserializing circuitry  135 . In one embodiment, the timing circuitry  133  includes a PLL (a delay-locked loop or even open-loop delay line may alternatively be used) to receive the incoming reference clock signal and, when the clock-enable signal is asserted, to generate an internal clock signal (e.g., a frequency equivalent or frequency multiple of the reference clock) that is used to sample command signals arriving via the command path and to synchronize operations within the interface die  125 , including data serializing and deserializing operations. More specifically, the internal clock signal generated by the PLL may be supplied to a clock tree that distributes multiple delay-matched instances of the clock signal to various other circuit blocks within the interface die  125 , including the command decoder  131 , data serializing/deserializing circuitry  135  and I/O circuitry  126 . 
     The command decoder  131  buffers incoming memory access commands, determines which of the storage arrays  104  a given command is directed to, and converts the command into the row and/or column control signals needed to carry out the commanded operation. In one embodiment, for example, each incoming memory access command may be either a row command (e.g., an activation command or a precharge command) that includes bank and row addresses that uniquely identify a bank and storage row therein to be activated (or bank to be precharged), or a column command that includes bank and column addresses that uniquely identify the bank for which a row has been activated (i.e., contents of row transferred to set of sense amplifiers for the corresponding bank) and a column offset within the activated row. In the case of a row command, the command decoder converts the received bank and row address values into a set of row control signals and queues the row control signals to be output, in parallel, via an appropriate one of memory array interfaces  137   1 - 137   4  (e.g., determined based on the bank address) a predetermined time (e.g., predetermined number of cycles of the internal clock signal) after the row command is received via the command interface  127 . Note that in an embodiment in which a storage bank is partitioned between two or more memory arrays of the storage die (e.g. elements  104   1 - 104   4  of  FIG.  1   ), the row control signals may be queued for output to more than one of the storage arrays simultaneously (i.e., and thus, output via more than one of the memory array interfaces  137   1 - 137   4 ). Similarly, in the case of a column command, the command decoder  131  converts the received bank and column address values into a set of column control signals and queues the column control signals to be output, in parallel, via one or more of the memory array interfaces  137   1 - 137   4  a predetermined time after the column command is received via the command interface  127 . 
     In the case of a memory write operation, write data and corresponding data mask information is received via the data I/O interface  129  and deserialized to form a more parallel (i.e., wider) write data word that is output to the storage die via the data path coupled to an address-selected one of the storage arrays (i.e., via the data portion of one of memory array interfaces  137   1 - 137   4 ). As an example, in one embodiment, write data is received synchronously in a sequence of 32-bit data transfers via the data I/O interface  129 , then deserialized to form a 128-bit write data word. The masking information (e.g., one mask bit per byte of write data) may be used to suppress output of selected bytes of the 128-bit write data word from the interface die  125 , thereby preventing the corresponding column locations within the storage die from being overwritten with write data. Alternatively, the masking information may be supplied to the storage die which itself may include circuitry to prevent data write in the indicated column locations. With respect to read and write data timing, in one embodiment, the data serializing and deserializing circuitry  135  may include read and write data queues to introduce a desired latency between receipt of a write command via interface  127  and data transfer via the internal data path (i.e., write data transferred via the data portion of memory array interface  137 ) or data I/O path  129  (read data). 
     As discussed above, splitting the high-speed interface circuitry and core storage circuitry between separate integrated circuit dice obviates process technology compromises, making it possible to fabricate high-speed interface circuitry in processes that yield faster, lower-gate-capacitance transistors and enabling the core storage circuitry to be implemented in processes that balance cell density and retention. The timing circuitry  133  and high-speed I/O circuitry  126 , in particular, tend to be come substantially more efficient when implemented in smaller-geometry processes.  FIG.  3   , for example, illustrates a portion of a inverter-based clock distribution circuit  140 A implemented in a conventional DRAM process (e.g., an XXnm, dual gate-oxide DRAM process, where “XX” would be, for example, “90” for mainstream processes, 110 for trailing edge processes or 80 for leading edge processes) and a counterpart inverter-based clock distribution circuit  140 B implemented in a high-speed logic process (e.g., a YYnm, 1P6M CMOS process, where “XX” would be, for example, “90” for mainstream processes, “130” for trailing edge processes, and “65” for leading edge processes). In the conventional DRAM process, inverter fan-out is generally more limited due to the slower, higher gate capacitance transistors and thus typically requires multiple inverter stages to achieve a desired fan-out. In the particular example shown, fan-out is constrained to two loads per inverter  141  so that, to achieve a total fan-out of eight, seven inverters  141  are used. By contrast, because of the faster switching speed and lower gate capacitance achieved within the smaller-geometry process, each inverter  143  may drive as many as eight loads so that a single inverter  143  may be used to provide the same signal drive capability as the seven inverters  141  in  FIG.  3   . Considering that all the inverters within the clock tree (and PLL and other interface circuitry) may be clocked near or above Gigahertz frequencies full-time during normal operation, the multi-fold reduction in clock tree and PLL components represents a substantial power savings within the multi-die memory module. 
     Another benefit of splitting the high-speed interface and storage core between separate integrated circuit dice is that data I/O connections may be provided separately to each storage array on the storage die, thus avoiding the need to route bit lines for each storage array to a centralized I/O circuit, as is the case when I/O circuitry is disposed centrally between multiple storage arrays in a memory IC. This approach is especially advantageous when combined with a 3D stacking technology (e.g., flip-chip bonding, thru-silicon via, die-in-substrate encapsulation, etc.), and/or a low-power, short-channel TO interface technology (e.g., AC-coupled interconnect), that does not require the memory array contacts to be positioned at the edges of the memory die.  FIG.  4   , for example, illustrates a comparison between a conventional arrangement of a storage array coupled to a centralized I/O circuit and an arrangement that may be used within the storage die  103  of  FIG.  1   . As shown, the bit lines  153  within the conventional storage array  151  extend across virtually the entire length of the storage array to couple storage cells  154  to a mid-die data I/O circuit  158 . By contrast, in a storage array  161  that may be used to implement any of the storage arrays  104   1 - 104   4  of  FIG.  1   , a dedicated data I/O circuit  165  may be provided and therefore may be disposed centrally within the storage array  161 . By this arrangement, the bit lines of the storage array  161  may be split into two half-length bit line segments  163 A and  163 B that each extend from an outermost row of the storage array  161  to the centrally located (e.g., disposed at or near the midpoint between outermost rows) data I/O circuits, thereby roughly halving the capacitance of the storage array bit lines and thus reducing the time required to retrieve data from storage cells  164  in the outermost rows (the worst case and therefore limiting retrieval time) and also reducing power required to precharge the bit lines. Note that, while not shown in detail, the I/O circuit  165  may include sense amplifier circuitry and bank/column decode circuitry, or may be coupled to sense amplifier circuitry within individual storage banks of the storage array  161 . 
       FIG.  5 A  illustrates an exemplary arrangement of storage arrays  187   1 - 187   4  within a storage die  185  and  FIG.  5 B  illustrates a more detailed embodiment of a representative storage array  187 . In the embodiment shown, the storage die  185  includes four storage arrays  187   1 - 187   4  (storage quadrants Q1-Q4), and eight storage banks, with each pair of cater-corner (i.e., diagonally opposed) storage arrays including the A and B segments, respectively, of a set of four storage banks. More specifically, odd-numbered storage quadrants Q1 and Q3 ( 187   1  and  187   3 ) collectively include even numbered storage banks B0, B2, B4 and B6, with bank segments B0-A, B2-A, B4-A and B6-A being disposed within quadrant Q1 ( 187   1 ) and bank segments B0-B, B2-B, B4-B and B6-B being disposed within quadrant Q3 ( 187   3 ). Odd numbered storage banks are similarly disposed in A and B segments within quadrants Q2 and Q4 ( 187   2  and  187   4 ). As in all other storage die embodiments described herein, there may be more or fewer storage arrays per storage die, and more or fewer storage banks per storage array. Also, each storage bank may span more or fewer storage arrays than shown in  FIGS.  5 A and  5 B . 
     Turning to  FIG.  5 B , each of the storage arrays  187  includes a row decode circuit (not specifically shown) that responds to a bank-sense signal (B Sense) by selecting one of the four storage bank segments  204   0 ,  204   2 ,  204   4  or  204   6  (specified by a two-bit row-bank select value, RBSel[1:0]), and activating one of 4096 rows therein specified by a 12-bit row address value, RAdr[11:0]. Together, the bank sense, row-bank select, and row address value constitute, at least in part, exemplary row control signals  200  (other embodiments may use different signals that achieve the same or similar functionality). More or fewer banks  204  per storage array  187  and/or more or fewer rows per bank  204  may be provided in alternative embodiments, in which case RBSel and RAdr values may have more or fewer constituent bits. In the row activation operation, the contents of the activated row are transferred to a bank sense amplifier circuit  207  to enable write and read operations in response to column control signals  201 . More specifically, when a column-latch signal (ColLat) is asserted, the sense amplifier circuit  207  for the bank  204  specified by a column-bank select value, CBSel[1:0], is coupled via array bit lines  208  to a column decoder  210  (or column multiplexer) circuit disposed centrally within the storage array  187 , and a column address value, CAdr[11:0], is applied to couple a selected one of 4096 columns of array bit lines  208  to a data I/O circuit  212 , thereby enabling write data received via the data I/O circuit  212  to be driven onto the selected column of array bit lines  208  to overwrite data within the corresponding column of sense amplifiers within a bank-selected sense amplifier circuit  207 , or enabling read data to be output from the column of sense amplifiers to the data I/O circuit  212  and thus output to the interface die. Together, the column-latch signal, column-bank select value, and column address value constitute, at least in part, exemplary column control signals  201  (other embodiments may use different signals that achieve the same or similar functionality). 
     Note that the individual storage arrays may be associated with different regions of a physical address space in a number of ways. For example, if there are sixteen storage arrays collectively within the set of storage dice, and the overall multi-die memory device is logically arranged as a four-bank device, then four storage arrays may be logically grouped together and associated with a single bank address. By this arrangement, a configurable number of storage banks may be established (e.g., through setting within a programmable register or other configuration circuit) and the total number of storage arrays dynamically allocated among each. 
       FIGS.  6 A and  6 B  illustrate embodiments of multi-component packages  220  and  250  having separate storage and interface dice as described above. In the multi-component package  220  of  FIG.  6 A , the interface die  227  and storage die  229  are disposed in a stack on a multi-component package (MCP) substrate  225 . In one embodiment, the substrate  225  is a non-conductive substrate having conductive vias therein to couple contacts of the interface die (the bottom die in the stack in this example) to ball grid array (BGA) contacts  237  for the multi-component package  220  (module contacts other than BGA may be used in alternative embodiments). The BGA contacts  237  may be soldered to counterpart landings on a daughterboard or motherboard (e.g., a memory module, blade, or motherboard of a data processing system, including various consumer electronics devices such as gaming consoles, mobile telephones, personal digital assistants (PDAs), cameras, audio and video rendering devices, etc.) and thus couple the multi-component package  220  to a larger electronics system. Within the multi-component package  220 , the interface die  227  may be wire-bonded to vias, traces or other conductive structures formed on or within the substrate  225  or may be coupled to the conductive structures via micro-BGA  231  or other flip-chip die-interconnect technology. The storage die  229  is disposed on top of the interface die  227  to form the die stack, and may be isolated from the interface die  227  by a dielectric spacer  230 . In the particular embodiment shown, the storage die  229  is wire-bonded ( 235 ) to conductive traces  233  disposed on the surface and/or sub-surface layers of the substrate  225 , the conductive traces  233  extending to the contacts of the interface die  227  to establish the intra-package interconnection between the interface die  227  and storage die  229 . Other 3D packaging approaches may be used to connect the interface die  227  with the substrate  225 , including, without limitation, thru-silicon vias, flex-tape, die-in-substrate encapsulation, direct wafer bonding, proximity interconnect, and so forth, with and without associated die-thinning techniques. A housing or cover  237  formed from plastic, ceramic or other non-conductive material may be disposed over the substrate, covering and protecting the die stack and interconnection structures. 
       FIG.  6 B  illustrates an alternative embodiment of a multi-component package  250  in which an interface die  253  and storage die  255  are disposed side-by-side on a “System-in-Package” substrate  251 . As in the embodiment of  FIG.  6 A , the substrate  251  may include conductive vias or other conductive structures to enable signal delivery via an external BGA  237  or other package interconnection technology, and may include conductive traces on the die-mount surface (or sub-surface layers) to which contacts on the storage die  255  and interface die  253  are wire bonded ( 258 ,  256 ) to establish die-to-die interconnection. The interface die  253 , storage die  255  or both may alternatively be mounted in a flip-chip arrangement instead of being wire-bonded to the substrate conductors. Also, as in the embodiment of  FIG.  6 A , a non-conductive housing or cover  260  may be disposed over the substrate  251  to protect the dice and interconnections structures. 
       FIG.  7 A  illustrates an embodiment of a multi-die memory device having an interface die  303  that may be configured at run-time or production time to establish a selected interface data width, data rate, and electrical signaling levels. In the particular embodiment shown, the interface die may include a run-time programmable register, production-time programmable configuration circuit (e.g., fuse-programmable or anti-fuse-programmable circuitry) or input-signal configuration circuit (i.e., configuration determined by external inputs which may be strapped to high and low logic levels or delivered by another device) to enable selection between a 32-bit wide data interface at 1.6 Gigabit per second (Gb/s), a 16-bit wide data interface at 3.2 Gb/s or an 8-bit wide data interface at 6.4 Gb/s. Circuitry to support other data interface widths and/or data rates may be provided in alternative embodiments. However configured, an interface selection signal, ISel, may be provided to the interface die  303  to establish the interface characteristics, thus permitting the multi-die memory device to be applied in a variety of applications, for example, in place of various different conventional memory devices. Regardless of the selected interface characteristics, the interface die converts command and data signals as necessary to carry out data storage and retrieval operations within storage die  301 , thereby enabling application of the same storage die  301  in a broad variety of applications and thus providing the potential for volume production savings. Note also that a single storage die design with multiple, independently accessible storage arrays can be combined and interfaced with many different interface die designs, each with the same type of “internal memory interface,” but different types of “external memory interface” each specific to a particular DRAM memory type with different bank counts and/or burst lengths (e.g., one that interfaces to standard DDR3 memory interfaces, another that interfaces to standard GDDR4 interfaces, etc.) to again provide the potential for volume production savings. Also, as the storage die design is suitable to be co-packaged with multiple storage die, the composite device formed by, for example, a 5-die stack (one interface die plus four storage die) design could be achieved that mimics a very high density DRAM device currently unachievable in the storage die&#39;s fabrication technology (e.g., a 4 Gb composite DRAM device can be constructed using DRAM die built in a 1 Gb DRAM fabrication technology). Also, as the storage die can be independently accessed, multiple storage die can be simultaneously activated to provide sufficient “core bandwidth” to meet the needs of the interface die&#39;s external “I/O bandwidth” requirements (e.g., two storage-die, each with maximum per-die bandwidth of 1.6 GBps, can be combined with an interface die to form a composite memory device that delivers 3.2 GBps externally). Also, the same storage die design can be packaged together with a highly integrated system-on-chip application-specific IC (such as a cell phone processor chip) which has particular memory requirements addressed by this storage die design (e.g., very low active power, simultaneous read/write access to different storage arrays, etc.). 
       FIG.  7 B  illustrates an exemplary serializing circuit  320  that may be provided within an interface die to support configurable serialization of read data returned from a storage die within a multi-die memory device. Though not specifically shown, a configurable deserializing circuit may be provided within the interface die to perform operations in reverse of those performed by the serializing circuit  320  and thus provide for read and write configurability of the high-speed interface data rate and data width. In serializing circuit  320 , a 32-bit portion ( 322 ) of a read data value (e.g., a 128-bit or larger column data value returned from a storage device), including bytes a0-a3, is latched within a first-stage storage buffer  321  in response to clock signal, ClkA. Byte pairs a0/a1 and a2/a3 are supplied to respective input ports of multiplexer  323  which responds to the level of ClkA (high or low in a given half clock cycle) to pass byte pairs a0/a1 and a2/a3 alternately to a second stage, two-byte storage buffer  325 . The second stage buffer  325  stores the byte pair forwarded in a given half cycle of ClkA in response to a clock signal, ClkB. ClkB oscillates at twice the frequency of ClkA so that both two-byte portions of the four-byte input  322  are stored per ClkA cycle. The two bytes stored within the second stage buffer, b0 and b1, are output to respective input ports of another multiplexer  327 , which in turn responds to the level of ClkB to pass bytes b0 and b1 alternately to a third stage, single-byte storage buffer  329 . The third stage buffer  329  stores the byte forwarded in a given half-cycle of ClkB in response to a clock signal, ClkC, having twice the frequency of ClkB so that all four of the originally received bytes a0, a1, a2 and a3 are stored in third stage buffer  329  in successive quarter-cycles of ClkA. As shown, the output of the third stage buffer  329  is provided, along with bytes b0 and a0 to respective input ports of output multiplexer  331 , which receives a 2-bit interface select signal ISel[1:0] at a control input. Bytes b1 and a1 are similarly provided to respective input ports of output multiplexer  333  which also receives the interface select signal. By this arrangement, the setting of the interface select signal (which may be configured through run-time program control, production-time setting and/or input-signal control as described above) may be used to select c0, b0 or a0 to be output via byte transmitter  341   1  and may similarly select bytes b1 or a1 to be output via byte transmitter  341   2 . Transmitters  341   3  and  341   4  are used to drive bytes a2 and a3, when used in a given interface configuration. As shown, transmitter  341   1  is clocked by transmit clock tClk1, transmitter  341   2  is clocked by transmit clock tClk2, and transmitters  341   3  and  341   4  are clocked by transmit clock tClk3. In this arrangement, each of the four byte transmitters  341   1 - 341   4  is enabled to output a respective byte of a 32-bit output data value when the interface select signal indicates a ×32, 1.6 Gb/s data interface. By contrast, when the interface select signal indicates a ×16, 3.2 Gb/s data interface, byte transmitters  341   1  and  341   2  alone are enabled to output data, 3.2 Gb/s data interface and, when the interface select signal indicates a ×8, 6.4 Gb/s data interface, byte transmitter  341   1  alone is used to output data. Table 340 shows exemplary clock rates, and the interface width and data rate for given values of the interface-select value. For example, if the interface select is set to ‘00’, a ×8 data width and 6.4 Gb/s data rate are selected, in which case, ClkC oscillates at 6.4 GHz (6.4 G), ClkB oscillates at half that rate (3.2 G) and ClkA oscillates at half the clock B rate (1.6 G). Accordingly, a 32-bit data value  322  is loaded into the first stage buffer  321  every 625 nanoseconds (ns), with byte pairs a0/a1 and then a2/a3 being shifted into second stage buffer  325  in successive halves of the 625 ns input data interval, and finally with bytes a0, a1, a2 and then a3 being shifted into third stage buffer  329  in successive quarters of the 625 ns interval. Accordingly, transmit clock, tClk1 oscillates at 6.4 GHz to enable byte transmitter  341   1  to transmit each byte of the four-byte sequence delivered via port ‘00’ of output multiplexer at a 6.4 GHz data rate. Because byte transmitters  341   2 - 341   4  are unused in ×8@6.4 Gb/s mode, transmit clocks tClk2 and tClk3 may be disabled and thus are shown in table 340 as “off.” 
     When a 16-bit data width at 3.2 Gb/s is selected (ISel[1:0]=01), third stage buffer  329  is unused and ClkC may be disabled as shown, while ClkA and ClkB continue to oscillate at 1.6 GHz and 3.2 GHz, respectively. In this arrangement, a 32-bit data value  322  is loaded into the first stage buffer in each 625 ns input data interval (i.e., while read data is being output), with byte pairs a0/a1 and then a2/a3 being shifted into second stage buffer in successive halves of the 625 ns input data interval, and delivered via the ‘01’ ports of output multiplexers  331  and  333  to byte transmitters  341   1  and  341   2 . As shown, transmit clocks tClk1 and tClk2 are both operated at 3.2 GHz to transmit each pair of bytes b0/b1 every 312.5 ns. Transmit clock tClk3 may remain disabled as byte transmitters  341   3  and  341   4  are unused in ×16@3.2 Gb/s mode. 
     When a 32-bit data width at 1.6 Gb/s is selected (ISel[1:0]=10), both the second and third stage buffers are unused and ClkB and ClkC may be disabled as shown. ClkA oscillates at 1.6 GHz to load a new 32-bit data value  322  into first stage buffer  321  every 625 ns. Bytes a0 and a1 are delivered to byte transmitters  341   1  and  341   2  via the ‘10’ ports of output multiplexers  331  and  333 , and bytes a2 and a3 are supplied to byte transmitters  341   3  and  341   4 . Transmit clocks tClk1-tClk4 are operated at 1.6 GHz to establish the 1.6 Gb/s data transmission rate. 
       FIG.  8    illustrates an alternative embodiment of a multi-die memory device  400  having multiple storage dice  402   1 - 402   N  coupled to a shared interface die  401 . In the embodiment shown, each of the storage die  402  has an asynchronous (i.e., un-clocked or clockless) control interface as discussed above and thus consumes substantially less static power than conventional integrated circuit memory die that include on-chip high-speed synchronous interface circuitry. Accordingly, storage capacity within the multi-die module  400  may be increased multi-fold without corresponding multiplication of the overall device power consumption. In one embodiment, each of the memory control interfaces  403   1 - 403   4  within the interface die  401  is coupled via a multi-drop control/data signal path  405  a respective storage array within each of the storage dice  402   1 - 402   N . Additional device-select control signals may be generated within the interface die  401  (e.g., based on address information received via high-speed interface  407 ) to select one of the memory dice  402   1 - 402   N  to respond to memory control signals on a shared path  405  during a given interval. Also, accesses to the memory dice  402  may be pipelined according to the deterministic data output times of the individual die  402  so that row operations (e.g., activation and precharge operations) may be performed in one or more of the memory dice  402  concurrently with column access operations (read or write operations) on one or more others of the memory dice  402 . Also, instead of shared data and control signal paths  405 , each of the storage arrays within each of the dice  402  may be coupled to the interface die  401  by a dedicated data path and/or control path. 
       FIG.  9    illustrates an alternative embodiment of a multi-die memory device  412  in which an interface die  415  includes a dedicated set of data interfaces for each storage die  416   1 - 416   N . In the particular embodiment shown, for example, each storage die  416  includes four storage arrays (Q1-Q4), with like numbered storage arrays coupled via respective point-to-point (i.e., dedicated two transmission between two endpoints as opposed to multi-drop) data paths  418  to corresponding dedicated data interfaces within control ports  417   1 - 417   4  of the interface die  415 . More specifically, the Q1 storage array within each of memory devices  416   1 - 416   N  is coupled via a respective point-to-point data path  418  to a respective data interface within control port  417   1  of the interface die, and the Q2-Q4 storage arrays are likewise coupled to respective data interfaces within each of control ports  417   2 - 417   4 . Although not specifically shown in  FIGS.  8  and  9   , control signals (including row and column control signals, and row and column address values) may be communicated either asynchronously or in conjunction with a command timing signal (such as a clock or strobe signal) to each of the storage arrays via a dedicated point-to-point control path (i.e., control path per storage array), or via a multi-drop control path shared among all of the storage arrays, or via one of several multi-drop control paths that are shared by respective subsets of the storage arrays. 
     In one embodiment the total number of signaling interconnects (wires or other conductive structures) required to provide the point-to-point signaling paths  418  between the interface die and the DRAM die shown in  FIG.  9    is reduced by time-multiplexing data transfer over the signaling paths. While this can be done in a straightforward manner for the unidirectional command and control interface (e.g., by using a conventional RAS/CAS DRAM control protocol), this presents particular challenges in the asynchronous storage dice  416  of  FIG.  9    as there is no ready timing reference available to time the multiplexed, bidirectional data transfer. That is, in contrast to conventional synchronous storage devices which receive a free-running clock signal (and thus may output data and, in some cases, corresponding timing strobe signals in synchronism with the clock signal), a free-running clock is purposely omitted in the storage dice  416  of  FIG.  9    to avoid power consumption during periods in which the storage dice  416  are not outputting data. In one embodiment, described in greater detail below, each of the storage dice  416  includes circuitry to output time-multiplexed read data in response to a signal, referred to herein as a demand signal, supplied by the interface die  415 . That is, after issuing a data read command directed to a given storage array (or set of storage arrays), the interface die  415  delays a predetermined time that corresponds to the time required for the requested read data to be retrieved from the array core, and then issues, via one or more signal paths, a sequence of demand signals to enable the storage array to responsively output a corresponding sequence of data chunks (or segments or components) that collectively form the requested read data word. By enabling the storage die data driver circuits only in response to assertion of the demand signal, time-multiplexed data transmission may be achieved with substantially reduced power relative to embodiments in which a free-running timing source is provided to (or generated within) the storage die. In effect, substantial transmission-related power consumption occurs only when data is demanded by the interface die  415 , rather than continually as in free-running clock embodiments. 
       FIG.  10    illustrates an embodiment of a multi-die memory device  420  in which an interface die  421  outputs a k-bit demand signal to a selected one of multiple storage dice  423   1 - 423   N  (or at least one such storage die) to enable read-data output. More specifically, the selected storage die  423  responds to incoming memory access requests (command/control signals) by carrying out the requested memory access within a storage core  424 , then buffering the data for transfer in a data input/output (I/O) circuit  425 . The buffered data may then be output in a stream of component values referred to herein as data units, with each data unit being transmitted in response to a respective edge of the demand signal. By this arrangement, all timing control and related circuitry may remain on the interface die  421 , enabling the storage die  423  to be constructed simply and without power-consuming clocking circuitry, and yet the storage die  423  may still output data at rates that rival those of modern synchronous memory devices. As shown, the interface die  421  issues control signals to a selected one of storage dice  423   1 - 423   N  via command/control path  426 , transfers data to and receives data from a selected storage die via data path  427  and issues demand signals to the selected storage die via demand path  428  (which may be a single signaling link). In one embodiment, the command/control path  426  may be coupled in multi-drop fashion to each of the storage dice  423   1 - 423   N , while dedicated, point-to-point data paths  427  and corresponding demand paths  428  are provided between the interface die  421  and each storage die  423 . In alternative embodiments, point-to-point command/control paths  426  (or some portion thereof) may be provided between the interface die  421  and each storage die  423 , and/or multi-drop paths may be used for data and/or demand signal transfer. Also, individual data paths  427 , demand paths  428  and/or command/control paths  426  may be shared by subsets of devices, thus establishing a limited number of communication endpoints for each signaling path. 
       FIG.  11    illustrates an embodiment of a timing arrangement for bi-directional data transmission between storage die  423  and interface die  421  via data path  427 . Referring first to data transmission from interface die  421  to storage die  423  (e.g., write data transmission), a timing signal (T) generated (or received) within the interface die  421  is supplied to a transmit circuit  433  which responds to edges in the timing signal by transmitting individual write data units via data path  427 . The timing signal is supplied to (and propagates through) delay element D1, driven onto demand path  428  by demand-line driver  429 , and then received within storage die  423  and supplied to data receiver  431  to time the sampling of the write-data units conveyed on data path  427 . In one embodiment, the data receiver  431  performs a deserializing function by combining a sequence of n-bit data units received in response to edges of the timing signal into an m-bit received data value, R×D (m being greater than n). Delay element D1 may be calibrated at production time, device initialization time and/or adaptively during device operation to align transitions in the timing signal as received at the input of the data receiver  431  with a desired sampling point (e.g., data eye midpoint) for the data waveforms conveyed via path  427 . 
     Still referring to  FIG.  11   , an m-bit read data value (T×D) is supplied to data transmitter  430  which, in turn, transmits a sequence of n-bit data units (each being a component of the m-bit read data value) onto data path  427  in response to a respective edge of a k-bit demand signal conveyed on demand path  428 . That is, the interface die  421  outputs a demand signal to the storage die  423  and thus provides a timing reference for initiating data transmission within the storage die, effectively demanding each data-unit transmission. In the embodiment shown, the timing signal T propagates through delay element D1 (though D1 may be bypassed for demand signaling operation) and is driven onto demand line  428  by demand line driver  429 , thus effecting demand signal transmission. The demand signal is supplied to data transmitter  430  within the storage die  423 , with each transition of the demand signal (e.g., each high-to-low transition and/or low-to-high transition) used to trigger transmission of a respective data unit within the set of read data units that constitute the read data value T×D. In one embodiment, the delayed timing signal output from delay element D1 is supplied to a second delay element D2 to yield a sampling signal (S) that triggers sampling operations within data receiver  432  to sample the read data units output by storage-die data transmitter  430 . As with D1, delay element D2 may be calibrated at production time, device initialization time and/or adaptively during device operation to align transitions in the sampling signal at the input of the data receiver  432  with a desired sampling point (e.g., data eye midpoint) for the data waveforms conveyed via path  427 . 
     In one embodiment, the storage die  423  includes control circuitry, not shown, to enable operation of data receiver  431  and data transmitter  430  at different times according to command/control signals received from the interface die  421 . For example, the control circuitry may enable the data receiver  431  to receive data in response to a timing signal conveyed via demand line  428  after receiving a data write command, and disable operation of the data transmitter  430  during the same interval. Similarly, the control circuitry may enable the data transmitter  430  to transmit data in response to demand signal transitions after receiving a data read command, disabling operation of the data receiver  431  during the same interval. On the interface die  421 , similar control circuitry, responsive to read and write commands from a memory controller, may alternately enable the data transmitter  433  and data receiver  432  to carry out the requested data transfer operations. In alternative embodiments, rather than re-use the existing data and demand signal paths, separate timing signal paths may be provided for write data timing (e.g., a data strobe path to convey a source-synchronous data strobe signal) than are used for the demand signal associated with read data timing. Also, the particular delay element configuration and timing signal timing may be different from that shown in  FIG.  11    and established by virtually any circuitry within the interface die  421  and/or storage die  423  that is capable of adjusting the phase of the outgoing timing signals (or timing signal used to initiate interface-die data reception or transmission) relative to data transmit intervals via path  427 . Also, while the demand signal may consist of a single electrical signal with an oscillation frequency of the desired serialized data rate, it may also be realized by two or more phase-offset signals, which are combined within the output multiplexer circuit of the storage die to achieve the serialized data rate. Further, as shown in  FIGS.  10  and  11   , as many as k demand signals may be asserted to initiate transmission of n data values, where k ranges from one to n. In one embodiment, for example, the ratio of n:k is 8:1, such that one demand signal is asserted for each byte of data transmitted during a given transmission interval. Other ratios of n:k may be used in alternative embodiments. 
       FIG.  12    illustrates a more detailed embodiment of a multi-die memory device  425  in which a demand signal is used to effect time-multiplexed read data transfer between an interface die  430  and a storage die  431 . Circuitry similar to that described in reference to  FIG.  11    for timing and effecting write data transmission may be included within the interface die  430  and storage die  431  but, to avoid obscuring the read data path, is not shown. The interface die  430  includes a command decoder  433 , scheduler  435 , command/address register  437  (CA Reg), timer  439 , demand sequencer  441  (Dem Seq) and delay element  443  (all of which may be included, for example, within the command decode logic  131  shown in  FIG.  2   ) as well as a data receiver  445  which samples incoming read data in response to a sampling signal  444  (i.e., a delayed version of demand signal  434 ) supplied by the delay element  443 . The storage die  431 , which may be the sole storage die or one of multiple storage dice within a multi-die memory device, includes command decode logic  457  (Cmd Decode) to receive command and address information from the interface die via command/address path  446 , and a data transmitter  459  (DQ Tx) to output read data to the interface die via data path  448  and in response to the demand signal  434  when driven onto demand path  450  (DEM) by driver  442 . Note that the interface die  430  and storage die  431  both may include additional circuitry (not shown) to support data write transactions, configuration operations and any of the various other operations described above. 
     The command decoder  433  responds to memory access commands (or requests) received via host command path  432  by generating corresponding memory access commands and address values that are queued for transmission in command/address register  437  and eventually driven onto command/address path  446  by command/address driver  438 . The command decoder  433  also signals the scheduler  435  to indicate command receipt and the nature of the command (e.g., read, write, configure, etc.) and thus enables the scheduler  435  to make decisions regarding the order and timing of command/data transmission to the storage die  431  and data receipt from the storage die. In particular, when a receipt of a memory read command is signaled by the command decoder  433 , the scheduler  435  asserts a launch signal  436  after an appropriate time delay (which time delay may depend, for example, on previously issued commands the transactions for which are in progress) to advance the memory read command to the head of the command/address queue (i.e, within the command/address register  437 ) and enable the memory read command and corresponding address to be output via the command address path  446 . As discussed, the command and address may be output concurrently via respective portions of the command/address path  446  or in two or more time-multiplexed transfers over the command/address path. 
     In the embodiment shown, the launch signal  436  is also supplied to the timer  439  which delays for a predetermined time that is set or calibrated to the elapsed time between receipt of the memory read command within the storage die  431  and output of corresponding read data from the storage array  455  within the storage die  431 . After the predetermined time has elapsed, the timer  439  asserts a demand-enable signal  440  to enable the demand sequencer  441  to issue a sequence of demand signals  434 . The demand signals  434  are supplied to the data transmission circuitry  459  of the storage die (i.e., via demand-strobe line  450 ) to enable transmission of a sequence of read data chunks and thus effect time-multiplexed output of a read data word  460  retrieved from the storage array  455  in response to the memory read command. The demand signals  434  are also supplied to the delay element  443  which generates, in response, a sequence of sampling signals  444  that are time delayed relative to the demand signals  434  according to the elapsed time between output of the first demand signal in the sequence and arrival of the first read data chunk at the data receiver  445 . The sampling signals  444  are supplied to the data receiver  445  as shown to sample the incoming sequence of read data chunks and thus receive the read data word output from the storage array  455  in response to the memory read command. After the sequence of read data chunks has been received, the demand signal  434  may be held at a steady-state (e.g., parked at a high or low level or at a midpoint between high and low levels) until another read data transfer is to be effected, thus avoiding unnecessary state changes within the storage die  431  (i.e., as would occur in the case of a free-running clock signal or other continually toggling timing source) and conserving power. 
       FIG.  13    illustrates an exemplary memory-read command sequence and corresponding read data transfer sequence within the multi-die memory device of  FIG.  12   . As shown, a memory read transaction is initiated when a read command  475  (COM) is received via the host command path  432  in  FIG.  12   . Unless the read command is directed to an already activated storage row within the storage die, a row activation command  477  is issued to the storage die via command/address path  446  in response to the read command from the host. If the read command is directed to an already activated storage row, the activation command may be omitted. In one embodiment, the row activation command  477  includes a row address strobe (RAS) signal (and is thus also referred to herein as a RAS command) and may additionally include a row address, deasserted write enable signal and any other signals for specifying a row activation. A predetermined time, tRC (i.e., a row activation time specified for the storage array), after issuance of the row activation command  477 , a column read command  479  is issued to the storage die via the command/address path  446 . In one embodiment, the column read command  479  includes a column address strobe (CAS) signal (and is thus also referred to herein as a CAS command) and may additionally include a column address, deasserted write-enable signal and any other signals for specifying a column read command. A first predetermined time after issuance of the column read command, tCC (i.e., a memory core timing constraint specified for the storage die), a second column read command  481  directed to a different column address within the activated row of data may be issued via command/address path  446  to initiate a second read operation. Also, referring to  FIGS.  12  and  13   , a second predetermined time after issuance of the column read command  479  (which may be the same as or longer or shorter than tCC), a read data word  460  becomes valid at an output of the storage array  455  and therefore available to be latched within the data transmitter  459  and output from the storage die. As shown, the timer  439  within the interface die  430  is set or calibrated to assert the strobe-enable signal  440  at a time such that an initial rising edge of the demand signal edge (i.e., a first demand signal assertion) arrives at the data transmitter  459  of the storage die  531  shortly after (or coincidentally with) valid data output from the storage array  455 . In one embodiment, the initial demand signal edge within a sequence or burst of demand signal edges latches the read data word  460  present at the output of storage array  455  within a word latch circuit of the data transmitter  459  and also enables a selected chunk of the data word to be driven onto data path  448 . Subsequent demand signal assertions, including falling-edges and rising edges of the demand signal are used to select remaining chunks of the data word to be driven onto data path  448  in sequence (i.e., one after another) as shown at  480 , thereby effecting time-multiplexed transmission of the entire read data word  460 . In the particular example shown, eight chunks of read data, numbered 0-7, are transmitted in succession (effecting an 8-chunk data burst) in response to eight transitions of the demand signal to effect time-multiplexed transmission of the read data word  460 . More or fewer demand signal transitions may be generated by the demand sequencer  441  in alternative embodiments to achieve smaller or larger burst lengths (i.e., more or fewer chunks per read data word transmission) or serialization ratios. Also, the burst length may be established by a one-time or reconfigurable setting within the interface die  430  (e.g., a programmable register setting). Further, while rising and falling edges of the demand signal are depicted as triggering data chunk output at the storage die, rising edges only or falling edges only may be used to trigger data chunk output in alternative embodiments. Also, while the demand signal is shown in  FIG.  12    as a single electrical signal with an oscillation frequency of the desired serialized data rate, it may also be realized by two or more phase-offset signals, which are combined within the output multiplexer circuit of the storage die to achieve the serialized data rate. 
     Still referring to  FIG.  12   , the second CAS command  481  results in assertion of an additional demand signal sequence and corresponding 8-chunk output data burst as shown at  482 . Additional CAS commands may be issued to effect additional back-to-back output data bursts. Also, as shown at  483  (during intervals in which no read data is to be transmitted), the demand signal may be parked at a logic low or high level to disable latching and data transmission operations within the storage die. The demand signal may also be parked at midpoint or other level between the logic low and high levels and, if desired or necessary, a preamble and/or postamble protocol established to indicate transmit-enable edges (i.e., edges that are used to enable latching and/or transmission operations within the storage die). 
     As discussed above, the sampling signal  444  (Samp) output by the delay element  443  is a time-shifted version of the demand signal, delayed according to the time required for data to propagate through the storage die output circuitry (i.e., data transmitter  459 ) and across the data path  448  to the data receiver  445 . The delay of the sampling signal relative to the demand signal may also include a quadrature delay component to establish the sampling signal transition at the midpoint of incoming data eyes as shown at  484 , thus ensuring that each data chunk conveyed in the incoming data signal is sampled during a data valid interval. Techniques for calibrating the delay element  443  to provide a desired timing relationship between the sampling signal  444  and incoming data are discussed below. 
       FIG.  14    illustrates an embodiment of a data transmit circuit  501  (DQ Tx) that may be used to implement data transmitter  459  of  FIG.  12    and its interconnection to a storage array  503  and demand path  450 . In one embodiment, the command decoder within the storage die generates a control signal  504  (Cntrl) in response to each CAS command after allowing any ongoing output data burst from a preceding CAS command to be completed. The control signal  504  is supplied to an asynchronous reset input (R) of a flip-flop  505  or other bi-stable device to lower a latch enable signal  506  (the flip-flop output) and thus a transparent mode (i.e., data flow-through) in latch  507 . By this operation, when a READ data word  502  (depicted as a 64-bit value in the embodiment of  FIG.  14   , though larger or smaller data words may be output from the storage array) becomes valid at the output of storage array  503 , the data word flows through the latch to the input of serializer  509 . In the particular embodiment shown, the demand path  450  is coupled to the clock input of flip-flop  505  and to serializer  509 . The data input of the flip-flip  505  is tied high so that, at the initial rising edge of a sequence of demand signal transitions, the flip-flop drives latch-enable signal  506  high to latch the read data word  502  within the transparent latch, thus maintaining availability of the read data word  502  for time-multiplexed transmission and at the same time enabling a subsequent memory transaction (e.g., a pipelined memory read or write operation) to be carried out within the storage array  503 . 
     Still referring to  FIG.  14   , the serializer  509  performs a parallel-load, serial-shift function, enabling each of multiple chunks of the latched data word (i.e., read data word within latch  507 ) to be output onto the external data path  448  (e.g., by output driver  512 ) in succession to effect time-multiplexed transfer of the entire read data word. In the implementation shown, the serialization data rate (i.e., relative to a system clock source, not shown) is controlled by the demand signal rate, and not by a timing signal synthesized by the storage die. In the particular embodiment shown, the serializer  509  supplies a sequence of eight byte-size data chunks (i.e., 8-bit values) to eight output drivers (collectively designated  512 ) in response to rising and falling edges of demand signals on each of four demand signal lines within demand path  450 . For example, each of the output drivers  512  may receive a respective one of the four demand signals and, on each transition of the demand signal (i.e., each rising edge and each falling edge), the output driver transmits a bit onto a respective line of data path  448 . By this operation, after eight transitions on each of the four demand signals, the entire 64-bit input word has been transmitted from the storage die to the interface die, where the actual data rate of that transmission is controlled by the interface die (i.e., by establishing the toggling rate of the demand signals). Note that longer or shorter burst lengths of differently sized chunks may be output in accordance with application requirements (e.g., chunk size may be programmed within the storage die and/or burst length may be programmed within the interface die). Also, though not specifically shown, the output drivers  512  may be enabled by assertion of the latch-enable signal (or a delayed version thereof) and tri-stated at other times to enable bi-directional data transfer over the external data path  448 . Also, the output drivers  512  may be integrated within the serializer  509  in alternative embodiments, as where multiple output drivers are enabled in succession to drive respective chunks of the latched data word onto the external data path. Also, as described previously, the demand signal as provided by the interface die to each output driver may consist of a single signal with a transition frequency at the desired serialized data rate, or it may consist of two or more phase-offset signals which collectively provide phase-offset transitions that correspond to the desired serialized data rate. 
       FIG.  15    illustrates an alternative embodiment of a serializer  523  and latch  521  that may be used to implement the serializer  509  and latch  507  of  FIG.  14   . Latch  521  includes a parallel input  522  to receive a 64-bit data word from a storage array (larger or smaller data words may be latched in alternative embodiments) and latches the data word in response to a high-going latch-enable signal (not shown). Latch  521  outputs eight data bytes (8-bit chunks) B0-B7 in parallel to the serializer  523  (as discussed there may be more or fewer chunks each having more or fewer constituent bits). The serializer  523  includes a multiplexer  525  and control circuit  527  (MuxCntrl) which cooperate to output each of the input data bytes in turn to each of the driver circuits or, if the multiplexer includes driver circuitry, onto an external signal path. In one embodiment, for example, the control circuit  527  responds to an initial transition of the demand signal by enabling a first output driver within multiplexer  525  to output byte B0 onto the external signal path, and then to a subsequent transition of the demand signal by disabling (e.g., tri-stating) the first output driver and enabling a second output driver within multiplexer  525  to output byte B1 onto the external signal path. Thereafter, subsequent transitions of the demand signal result in like disabling of the currently active output driver and enabling of the output driver for the next byte in the data transmission sequence. The individual output drivers may be coupled in a wired-OR to the output contact. In an alternative embodiment, the control circuit  527  may issue a sequence of multiplexer control signals to the multiplexer  525  to switchably pass each of the input bytes, in sequence, to a shared output driver (not shown in  FIG.  15   ) for transmission in successive time intervals. In one embodiment, multiplexer  525  is implemented by a pulsed signaling multiplexer as described in greater detail below. 
     As discussed in reference to  FIG.  12   , a timing calibration may be performed to enable the interface die to determine the appropriate time delay between assertion of a demand signal and assertion of a corresponding sampling signal to sample the read data value output in response to the demand signal.  FIGS.  16 A and  16 B  illustrate an exemplary timing calibration operation that may be carried out by the interface die  430  of  FIG.  12    to determine an appropriate time delay between assertion of demand signal  434  and assertion of read data sampling signal  444 . In general, the approach of  FIGS.  16 A and  16 B  involves sweeping the delay setting (and thus the propagation delay) of delay element  443  through a sequence of delays to identify a range of delay settings within which data may be reliably read from the storage die  431  and then establishing a desired timing offset at the midpoint within the range. In one embodiment, a known data pattern is read from the storage die  431  (e.g., from a pre-loaded register, a hardwired test value, or pre-loaded location within the storage array  455 ) and compared with the expected value to determine a pass or fail result for each delay setting. Referring to  FIG.  16 A , then, at  551  a minimum timing offset (i.e., delay setting) is established within the delay element, and then the known data pattern is read at  553 . The read data is compared with expected data in decision block  555  and, if no match is detected, the timing offset is advanced at  557  and the data read and compare operations at  553  and  555  are repeated. Note that the data read operation at  553  may involve numerous reads to ensure that, if a match is detected, the match is not a statistical aberration or that the timing offset is so near the edge of the desired range that one or more subsequent data reads at the same timing offset will yield failing results. 
     Referring to  FIGS.  16 A and  16 B , the timing offset is iteratively advanced from the minimum timing offset  579  until, when a data match is finally detected at decision block  555 , a lower timing offset is reached  571 . At this point, the lower timing offset is recorded in a temporary register at  559 , the timing offset is advanced at  561  and data read and compare operations  563  and  565  are performed to determine whether an upper timing offset has been reached. That is, if a data mismatch is not detected at  565 , then the timing offset is deemed to remain in the passing range (between lower timing offset  571  and upper timing offset  572  as shown in  FIG.  16 B ) and the timing advance, data read and compare operations ( 561 ,  563 ,  565 ) are repeated iteratively until a data mismatch (i.e., failing result) is detected. When a data mismatch is detected, the timing offset applied just prior to the mismatch detection (i.e., the most advanced timing offset at which no data mismatch occurred) is recorded as the upper timing offset at  567 , and then a final desired timing offset is determined at  569  based on the upper and lower timing offsets. In the particular embodiment shown, for example, the upper and lower timing offsets are averaged to determine a desired timing offset  575  at the midpoint of the passing range (e.g., as shown in  FIG.  16 B ), though the upper and lower timing offsets may be applied in various alternative ways to establish desired timing offsets that are advanced or delayed relative to the midpoint of the passing range. In any case, after the desired timing offset is determined, the desired timing offset is applied within the delay element  443  to control the delay between outgoing demand signal edges and corresponding edges of the receive data sampling signal. 
     Depending on the system timing margin, the calibration operation of  FIGS.  16 A and  16 B  maybe performed during system production to establish a one-time programmed delay value, or may be performed one or more times during device run-time to establish a dynamically controlled delay value. For example, in one embodiment, the calibration operation may be performed at device startup to establish the desired timing offset, and then left alone thereafter or repeated periodically or in response to certain events. In a particular implementation, for instance, the calibration operation may be carried out as frequently as necessary to compensate for temperature and voltage-induced timing drift and/or may be performed concurrently with refresh operations or other maintenance operations within the storage die. Also, while a linear search has been described (i.e., stepping the timing offset incrementally through a range of values), various alternative approaches for determining a desired timing offset may be applied, including binary or other non-linear searches, coarse/fine searches (i.e., coarse-stepping of the timing offset to identify the pass/fail boundaries at either end of the passing range, followed by fine-stepping of the timing offset within the coarse steps across the boundaries), and techniques that seek to minimize bit error rate or optimize other statistical results. Also, while calibration of the delay imposed by delay element  443  has been described, similar calibration operations may be carried out to determine the time delay imposed by timer  439  (i.e., how long to wait before asserting strobe-enable signal  440 ) or any other timing-dependent operations within the multi-die memory device. For example, the storage die  438  may contain a “feedback path” transmitter circuit, representative of the storage die&#39;s other transmitter circuits, which the interface die  430  can utilize within a closed-loop timing system to calibrate the required delay of delay-element  443 . In other embodiments, to minimize the amount of timing calibration circuitry, the calibrated delay value for one chip-to-chip interface can be simultaneously applied to several other like chip-to-chip interfaces. 
     In multi-die memory device embodiments described thus far, the interface die is used to control timing and data access operations within one or more storage die. In those embodiments and others discussed below, the interface die may additionally include circuitry to control various other operational aspects of the storage die. Referring to  FIG.  17 A , for example, an interface die  601  may include a variable-output voltage regulator  605  (Signaling Voltage Regulator) to provide one or more supply voltages to output drivers within the storage die  603  and thus control the amplitude of output signals generated by the storage die  603 . In the particular embodiment shown, the interface die  601  generates a supply voltage, V SWING , which is provided to the storage die through contact  608  (or other interconnect structure) and used to power output driver  609 , thereby enabling output driver  609  to generate waveforms having amplitudes determined by the interface die as shown in  FIG.  17 B  (i.e., V SWING  may be set to any of voltages V 1 -V n  to establish the output voltage swing impressed on line  612  via contact  610 ). In alternative embodiments, the interface die  601  may generate both upper and lower voltages used to power the output driver  609 . Also, instead of providing a supply voltage, the interface die may source or sink a driver biasing current. Similarly, though an inverter-type output driver  609  is depicted, virtually any type of output driver may be powered by the interface die  601  including, for example and without limitation, differential or single-ended, current-mode or voltage-mode, AC-coupled or DC-coupled output drivers. In yet other embodiments, the interface die  601  may provide a control value that is supplied to one or more digital-to-analog converters (DACs) within the storage die  603  to generate one or more supply voltages or currents for controlling the common mode and/or signal swing of the storage die output drivers. The control value may be applied directly to the DAC(s) or may be stored within a programmable register or other configuration circuit within the storage die  603 . With regard to calibration, searching strategies similar to that described in reference to  FIGS.  16 A and  16 B  (including variations thereof) may be used to determine a desired current and/or voltage supply level. For example, the supply voltage and/or current may be stepped through a range to identify a threshold at which data is reliably received, and then set to the threshold (multiplied by a safety factor, if desired). Also, though only a single supply output is depicted, the interface die  601  may generate multiple supply outputs for respective storage dice  603 , or for output drivers associated with respective storage arrays within a given storage die, or even for individual output drivers or groups of output drivers associated with a given storage array. 
     To mitigate the “known good die” (KGD) problem (also known as the “compound yield” problem) generally associated with multi-die packages, the interface die within a multi-die memory device may also be used to control mapping of redundant rows and/or columns onto defective or suspect rows/columns of storage cells within a counterpart storage die. That is, in contrast to conventional techniques in which relatively large (and therefore expensive in terms of consumed die area) laser fuses or other one-time programmable structures are provided within a storage device to support production-time selection between a suspect row or column and a redundant counterpart, a much smaller programmable register or other run-time configurable structure may be provided within the storage die and loaded (i.e. programmed) with one or more redundancy control values at device startup. The redundancy information may be stored, for example, within a non-volatile storage circuit within the interface die or within another die (e.g., a separate non-volatile storage die within the multi-die package) that is coupled to provide the redundancy information to the interface die. Also, the storage die may receive the redundancy information in the form of control signals passed via the control interface (e.g., the interface used to issue row, column and other memory-related commands or requests) or via a separate interface. Referring to the embodiment of a multi-die memory device depicted in  FIG.  18   , for example, interface die  640  may include a built-in-self-test (BIST) engine  645  to execute various self-tests directed to circuitry on the interface die  640  and on storage die  641  (e.g., pattern generation, pattern comparison, memory write/read/modify tests, retention tests and various other tests similar to those performed at wafer sort, burn-in, and final test in conventional memory devices), and thus may identify defective or unreliable rows and/or columns of storage cells within storage die  641 . In one embodiment, the BIST engine  645  issues programming instructions to the storage die (e.g., communicated by serial-port controller  647  to counterpart serial port controller  651  on the storage die  641 ) to establish settings within programmable register  653  to control the selection (shown conceptually by multiplexer  655 ) between defective/unreliable rows or columns (F) and redundant rows or columns (R). Defective or unreliable rows/columns within the storage die  641  may alternatively (or additionally) be identified during device production test and mapping between such rows/columns and their redundant substitutes programmed within an optional e-fuse bank (or other non-volatile storage, including on a non-volatile storage die co-packaged along with the interface die and the storage-die) of the interface die  640 . In such an embodiment, the e-fuse redundancy mapping may be output to the storage die  641  at device startup (e.g., via serial port controllers  647  and  651 ) to establish settings within register  653  to control redundant row/column selection. In other embodiments, defective row/column information identified during production test can be stored within computing equipment associated with the production test environment. This defective row/column information can then be used to determine redundancy maps which are loaded into the final composite device&#39;s non-volatile storage during or after final assembly. In one embodiment, the multiplexers associated with each row repair domain (e.g., there may be one redundant row for every megabyte of DRAM storage array) are connected in shift-register series, thus forming a “scan chain” arrangement. To assign a row redundancy control value, the interface die may “scan in” (or shift in) the desired value. A similar approach can be used to control column redundancy multiplexers. In any case, relatively large, production-time programmable structures such as laser fuses may be omitted from the storage die  641  (or at least reduced in number) without sacrificing yield-enhancing redundancy features (additionally, if the non-volatile storage is re-programmable, a failing DRAM device can potentially be repaired in the field). Accordingly, a larger percentage of the die area is available for implementing the storage array  657  (and/or for additional redundant rows and/or columns of storage cells), thus potentially reducing the per-bit cost of the storage die  641 . 
       FIG.  19    illustrates an embodiment of a multi-die memory device in which interface die  671  includes a power regulator  675  to selectively power each of multiple storage arrays  681   1 - 681   4  within a storage die  673  (or multiple storage dice), thereby enabling unused storage arrays  681  to be switched off (i.e., powered down) to conserve power. In the embodiment shown, the interface die  671  includes an allocation map  677  that indicates which of the storage arrays  681  are in-use (i.e., used to store data) at a given time, and that outputs a set of enable signals  676  to the power regulator  675  to enable or disable power delivery to the storage arrays  681  accordingly. In one implementation, the allocation map  677  is cleared upon device power up, and then updated in response to host memory write commands. As memory write operations extend to each additional storage array  681  within storage die  673 , the allocation map asserts the corresponding enable signal  676  for the storage array to enable power delivery thereto. In one embodiment, the interface die  671  may additionally receive deallocation notices or information from the host processor (or memory controller or other control entity) and may power-down storage arrays  681  in which all previously allocated memory space has been deallocated and thus are no longer in-use. 
     Still referring to  FIG.  19   , the allocation map  677  may indicate in-use regions of the storage die  673  with sufficient granularity to enable selective refreshing of storage rows therein. For example, in one embodiment, the allocation map  677  includes a number of array-map registers that correspond to respective storage arrays  681  within the storage die  673  (or storage dice), with each array-map register having a number of bits that correspond to respective rows of storage cells within the counterpart storage array. By this arrangement, individual bits of a given array-map register may be set or reset to indicate whether the corresponding storage row is in use (i.e., bits set or reset according to memory write requests and, if provided, deallocation notices from the host) and the in-use information  678  output to a refresh controller  679  to enable refresh operations to be bypassed for unused storage rows. Accordingly, refresh operations may be directed only to in-use storage rows, thereby saving power within the multi-die memory device relative to embodiments in which refresh operations are indiscriminately directed to all storage rows in sequence. 
       FIG.  20 A  illustrates an exemplary packaging arrangement that may be used to encapsulate a pair of storage dice  702   1 ,  702   2  within a multi-die memory device  725 . As shown, the multi-die memory device  725  includes a module substrate  727  having conductive interconnection structures (e.g., traces, vias, etc.) generally as described in reference to  FIGS.  6 A and  6 B . The interface die  701  and a first storage die  701   1  are disposed on the substrate  727  and coupled to one another as described above (e.g., via wire bond or flip-chip interconnects), and a second storage die  702   2  is disposed on top of the first storage die  702   1  to form a die stack. A cover or housing  728  may be disposed over the dice  701 ,  702  and interconnection structures, and secured to the substrate  727 . Though not specifically shown, a dielectric spacer may be disposed between the first and second storage dice to isolate the die from one another. Also, in an embodiment in which the first storage die  702   1  is wire-bonded conductive interconnect structures in or on the module substrate  727 , the first and second dice  702  may be offset from one another as shown (i.e., offset from a centerline that extends through the stack and normal to the substrate) to expose edges of the dice  702  for wire-bond access. As shown in embodiment  730  of  FIG.  20 B , additional storage dice  702   2 - 702   N  may be added to the die stack (thus achieving a stack of dice  702   1 - 702   N ) and offset from one another to enable wire-bond access to each. A cover or housing  732  may be disposed over the interface die  735  and storage dice  702 , and secured to module substrate  736 . 
       FIG.  20 C  illustrates another packaging embodiment  740  in which an interface die  745  and storage dice  702   1 - 702   N  are disposed in separate integrated circuit packages  741 ,  743  that mate to one another to form a multi-package module. In this approach, the external, electrical interface protocol (i.e. the DRAM “flavor”) can be selected at final assembly by the memory module manufacturer, rather than during memory die fabrication by the DRAM vendor. Although a package-on-package implementation is shown, a package-in-package arrangement may be employed in alternative embodiments. Also, a single storage die  702  may be disposed within the storage die package  741  instead of multiple storage dice  702  as shown. Further, instead of staggering the storage dice  702  to enable wire-bond access, other interconnection schemes and/or die stacking arrangements (including, but not limited to, thru-silicon vias, flex-tape, die-in-substrate encapsulation, direct wafer bonding, proximity interconnect) may be used. The package-to-package interconnections  747  may be established by direct electrical contacts (e.g., ball grid array, micro-ball grid array, spring contacts, pad-to-pad contacts and the like), or by contactless interconnects such as capacitive or inductive interconnects. 
       FIG.  20 D  illustrates yet another packaging embodiment  750  in which an interface die  755  is mounted in a flip-chip configuration with contact pads mated via micro-ball-grid array or other contact technology to counterpart landings on a module substrate  753  and thereby interfaced (e.g., through traces on and/or within the module substrate  753 ) to wire-bond interconnections to one or more storage dice  702   1 - 702   N  stacked above the interface die  755 . The entire stacked die arrangement may be encapsulated within a housing  751 , molding or other protective structure. 
       FIG.  20 E  illustrates a package-on-package (PoP) embodiment  760  having a storage package  762  stacked on an interface package  761 . The storage package  762  includes a substrate  763  having storage die  7021 - 702 N stacked thereon and encapsulated within molding or housing  765  as generally described above. The interface package  761  includes an interface die  767  wire-bonded or flip-chip mounted (or otherwise coupled) to substrate  769  and encapsulated within molding or housing  764 . Solder balls  768  (or any other interconnection structures) may be used to form electrical contacts between the interface package  761  and storage package  762 . 
       FIG.  20 F  illustrates an alternative embodiment of a package-on-package embodiment  770  having one or more storage packages  772   1 ,  772   2  stacked on an interface package  771 . In contrast to the embodiment of  FIG.  20 E , an interface die  777  is mounted on the underside of a substrate  779  (and optionally encapsulated within housing or molding  773 ) to form interface package  771 , and storage die  702   1  is similarly mounted on the underside of substrate  776   1  in storage package  772   1 . By this arrangement, lower profile interconnects  778  (e.g., micro-balls or other low-profile interconnects) may be used to electrically couple the first-level storage package  772   1  to second-level storage package  772   2  and thus reduce package height relative to a device having a stack of same-orientation storage packages  772 . One or more storage additional storage packages  772  (not shown) may be stacked on top of storage package  772   2  to increase the overall package storage capacity. The storage packages  772  may be constructed generally as described in reference to  FIG.  20 E , each having a substrate  776  and at least one storage die  702  (each or any of the storage packages  772  may have multiple storage dice as, for example, in the embodiment of  FIG.  20 E ) encapsulated within housing or molding  774 . In the embodiment shown, electrical interconnections between the interface package  771  and first-level storage package  772   1  may be formed, for example and without limitation, by solder balls  775  or other contacts. 
       FIG.  21    illustrates an embodiment of a memory module  800  having rows of multi-die memory devices  801  disposed on front and rear faces of a substrate  803  (the devices on the rear face of the substrate being shown in dashed outline). Traces disposed on the substrate  803  (including traces on submerged layers of the substrate) are used to convey signals between an edge connector  804  of the module and the multi-die memory devices  801 . Because each of the multi-die memory devices  801  may be designed to mimic the operation of various conventional memory devices, the memory module  800  itself may be pin compatible with memory modules populated by conventional devices. Accordingly, the memory module  800  may be installed in connector sockets in place of conventional memory modules, for example to reduce power consumption and/or increase capacity within a memory system. Although eight multi-die memory devices  801  are shown on each face of the module  800 , more or fewer devices may be provided according to interface or data width demands. For example, a ninth memory device  801  may be provided within each row to store error correction code (ECC) or other error-detection/correction data for the contents of the remaining memory devices  801  in the row. Also, while not specifically shown, a non-volatile storage such as a serial-presence-detect (SPD) memory may be disposed on the memory module to store characterizing information regarding the multi-die memory devices, including their programmable functions (e.g., interface programmability as described above), storage capacity, data rate capability and so forth. 
       FIG.  22    illustrates a memory subsystem  850  that includes a memory controller  870  and a pair of multi-die memory devices  803   1 ,  803   2  disposed in a package-on-package arrangement. In the particular embodiment shown, each of the memory devices  803  includes an interface die  855  and a single storage die  857  disposed in a stack as generally shown in  FIG.  20 D , though any of the multi-die memory device embodiments discussed above may alternatively be used, including those with multiple storage dice. Also, with respect to the package-on-package coupling via interconnects  861 , the multi-die memory device  803   2  is disposed in an inverted arrangement to take advantage of the cavity formed by module-to-module interconnection solder balls  863  and thus reduce the overall height of the package-on-package memory subsystem  850 . The memory controller  570  includes a control logic die  864  that may be a dedicated memory controller, or an application specific integrated circuit (ASIC) that includes functions other than (or in addition to) memory control including, without limitation, cell phone baseband processor, graphics pipeline support, bus bridge, processor-local-bus interface and so forth. Alternatively, the memory controller  570  may be part of a general-purpose or special-purpose processor or controller. As shown, the memory controller  570  may also be disposed in an inverted configuration to take advantage of the cavity formed by module-to-circuit-board interconnection balls  865  and thus reduce the overall height of the package-on-package memory subsystem. Although not shown, a housing or other structure may be partially or completely formed or molded over the package-on-package arrangement of  FIG.  22    to provide heat dissipation (cooling) and/or structural integrity. 
     In other embodiments, additional multi-die memory devices and/or other integrated circuit packages may be mounted in the package-on-package stack to provide additional memory capacity or other functionality. Also, while the interface die in the various embodiments described above has been described in terms of its function as an intermediary between one or more storage die and an external device such as a memory controller or processor or ASIC (application-specific integrated circuit) having a memory control function, the circuitry that constitutes the interface die may be implemented on the same die or in the same integrated circuit package as a memory controller, processor (e.g., a central processing unit, graphics processing unit, digital signal processing unit, etc.), ASIC or the like. As discussed, this allows potential cost savings to ASIC manufacturers by enabling a low-power DRAM design die design suitable for System-in-Package integration to also be shipped in high-volume, industry-standard DDR memory markets. 
       FIG.  23    illustrates an embodiment of a pulsed signaling multiplexer  870  that may be used to implement output multiplexers and/or serializing multiplexers in the various integrated circuit devices and systems described above, including multiplexer  525  within the data serializing circuit of  FIG.  15   . As shown, multiplexer  870  includes timing circuitry  878  having a plurality of timing circuits  880   a - n  coupled to transmitter circuitry  872 . The transmitter circuitry includes an array of AC-coupled transmitter circuits  874   a - n  that generate pulsed output signals. A common output node  876  receives the plurality of transmitter output signals in a time-multiplexed manner as more fully described below. By transmitting signals in this fashion, significant improvements in signal throughput and power efficiency for integrated circuits may be realized. 
     Still referring to  FIG.  23   , the plurality of AC-coupled transmitters  874   a - n  may be disposed in a parallel configuration with respective outputs tied together to the common output node  876 . For purposes of clarity, only one transmitter  874   a  will be described in detail, it being understood that all of the transmitters may be substantially similar in construction. Each transmitter includes an amplifier circuit or driver  882  such as a CMOS inverter, for example. The output of the driver feeds an AC-coupling element such as a series capacitor  884  that includes an output terminal  886  for directing an AC output signal to the node  876 . Each series capacitor  884  may have a capacitance on the order of around 50-150 fF (femto-Farads), and may be manufacturable through standard CMOS fabrication techniques. Moreover, it should be understood that, depending on the application, the on-die AC-coupling element may comprise a portion of a series capacitor, that for example, may cooperate with another portion of a series capacitor at a receiver end, or as part of the package assembly process (e.g., by using redistribution layer metal to form the top plate of a capacitor) to effect an entire capacitor structure. This enables flexibility for chip-to-chip applications where, for example, the contactless interconnect between two adjacent integrated circuits may be a series capacitor structure. Other alternatives are available as well, such as inductors to effect inductive coupling between chips. 
     The timing circuitry  878  provides signal offsets for input to the plurality of transmitter circuits  874   a - n .  FIG.  24    illustrates one embodiment of the timing circuitry, generally designated  900 , for use with the transmitters described above. A plurality of flip-flops  902   a - n  are disposed at each transmitter input (not shown), and have respective data input lines  904   a - n  and demand lines  906   a - n  (collectively forming an N-bit demand path  909 ) to receive independent data and demand signals. In one embodiment, a multi-phase clock generator or source  908  within interface die  907  outputs N demand signals on demand lines  906   a - 906   n , respectively, with the demand signals being offset in phase by desired phase increments. The phase offset demand signals are then fed to the clock inputs for the flip-flops  902   a - 902   n  as shown. Suitable multi-phase clock generators may be realized, for example and without limitation, using simple delay lines, oscillator-fed delay-locked-loop (DLL) circuits, or phase-locked-loop (PLL) circuits, where offset clock signals may be tapped following each delay element in a delay line (for the DLL), or each element in a ring oscillator (for the PLL). 
     Alternatively, the timing circuitry  908  may comprise a plurality of programmable or variable delay elements (not shown) to offset data signals being input to the transmitter circuitry  872 . Static weighted delay elements might also be used to provide the different delays. Additionally, while the timing circuitry described above is implemented upstream of each AC-coupled transmitter input, similar benefits may be realized by employing the timing circuitry between the outputs of the drivers and the series capacitors. 
     Referring again to  FIG.  23   , to maximize the bandwidth of the transmission channel, the multiplexer described above may employ termination circuitry  890  in the form of a termination resistor Rterm coupled between the node  876  and a termination voltage terminal Vterm (shown in this embodiment as DC ground). For applications involving relatively short transmission channel lengths, such as “system-in-package” (SiP) environments or other multi-component packages as discussed above, the termination resistor Rterm may be realized by an on-chip resistor implementation. The termination resistor may be realized through many different alternative embodiments, including single or multiple resistor implementations, transistor circuitry to effect a resistive output, and the like. 
     Due to the loading of multiple capacitive elements in parallel, the signal amplitude on node  876  generated by any one of the individual AC transmitters is reduced compared to how the transmitter would perform in isolation. However, due to the non-zero output impedance of the driver circuit  882 , the attenuation effect can be kept to reasonable levels. In an alternative embodiment, the output impedance of the driver circuit  882  may be increased, thereby decreasing the signal attenuation effect, by employing a tri-state driver in each transmitter  874 . Such drivers are configured to exhibit a high impedance output when operating in a non-driving mode. 
     In some applications, electrostatic discharge (ESD) protection circuitry  130  may be disposed in parallel with the termination resistor Rterm. The ESD circuitry may include a pair of reverse-biased diodes D1 and D2 tied between the node  876  and the termination voltage Vterm. Due to the AC-coupled natured of the pulsed signaling multiplexer  870 , the ESD circuit complexity may be minimized, which can substantially reduce DRAM die cost by reducing the die size overhead associated with the external interface system on the DRAM die. 
     In one embodiment, the pulsed signaling multiplexer  870  and its supporting circuitry may be realized by circuitry employed on a single integrated circuit. In other embodiments, one or more support circuits employed by the multiplexer may be implemented on a second integrated circuit. 
     In operation, data signals are fed along independent data paths to the timing circuitry  878 , where they are re-timed (or offset). The re-timing allows the multiplexer transmitters  874   a - n  to receive at their inputs data signals that are precisely offset in phase with respect to each other.  FIG.  25    illustrates an example of the timing relationships between the input data fed from the timing circuitry to the AC-coupled transmitters  874   a - n , and the combined output data pulse stream at the common node  876 . 
     As shown in  FIG.  25   , each transmitter signal output may be offset by an incremental phase. Due to the high-pass filtering nature of the series capacitor, the transmitter output comprises a brief pulse corresponding to the rise and fall times of the input data edge transitions. Since only signal transitions appear at the output of each transmitter, pulses appear on the output node for each signal transition in an “wired-OR” manner. This, in effect, provides a dramatic increase in the signaling rate at the output node  876 . In one embodiment, where eight transmitters may be arrayed in parallel with a single output, and offset in phase by ⅛ a symbol period (half the multi-phase clock period), a very low power parallel-to-serial transmitter circuit is achievable. 
     It should be noted that the various integrated circuits, dice and packages disclosed herein may be described using computer aided design tools and expressed (or represented) as data and/or instructions embodied in various computer-readable media, in terms of their behavioral, register transfer, logic component, transistor, layout geometries, and/or other characteristics. Formats of files and other objects in which such circuit expressions may be implemented include, but are not limited to, formats supporting behavioral languages such as C, Verilog, and VHDL, formats supporting register level description languages like RTL, and formats supporting geometry description languages such as GDSII, GDSIII, GDSIV, CIF, MEBES and any other suitable formats and languages. Computer-readable media in which such formatted data and/or instructions may be embodied include, but are not limited to, non-volatile storage media in various forms (e.g., optical, magnetic or semiconductor storage media) and carrier waves that may be used to transfer such formatted data and/or instructions through wireless, optical, or wired signaling media or any combination thereof. Examples of transfers of such formatted data and/or instructions by carrier waves include, but are not limited to, transfers (uploads, downloads, e-mail, etc.) over the Internet and/or other computer networks via one or more data transfer protocols (e.g., HTTP, FTP, SMTP, etc.). 
     When received within a computer system via one or more computer-readable media, such data and/or instruction-based expressions of the above described circuits may be processed by a processing entity (e.g., one or more processors) within the computer system in conjunction with execution of one or more other computer programs including, without limitation, net-list generation programs, place and route programs and the like, to generate a representation or image of a physical manifestation of such circuits. Such representation or image may thereafter be used in device fabrication, for example, by enabling generation of one or more masks that are used to form various components of the circuits in a device fabrication process. 
     In the foregoing description and in the accompanying drawings, specific terminology and drawing symbols have been set forth to provide a thorough understanding of the present invention. In some instances, the terminology and symbols may imply specific details that are not required to practice the invention. For example, any of the specific numbers of bits, signal path widths, signaling or operating frequencies, component circuits or devices and the like may be different from those described above in alternative embodiments. Also, the interconnection between circuit elements or circuit blocks shown or described as multi-conductor signal links may alternatively be single-conductor signal links, and single conductor signal links may alternatively be multi-conductor signal lines. Signals and signaling paths shown or described as being single-ended may also be differential, and vice-versa. Similarly, signals described or depicted as having active-high or active-low logic levels may have opposite logic levels in alternative embodiments. Component circuitry within integrated circuit devices may be implemented using metal oxide semiconductor (MOS) technology, bipolar technology or any other technology in which logical and analog circuits may be implemented. With respect to terminology, a signal is said to be “asserted” when the signal is driven to a low or high logic state (or charged to a high logic state or discharged to a low logic state) to indicate a particular condition. Conversely, a signal is said to be “deasserted” to indicate that the signal is driven (or charged or discharged) to a state other than the asserted state (including a high or low logic state, or the floating state that may occur when the signal driving circuit is transitioned to a high impedance condition, such as an open drain or open collector condition). A signal driving circuit is said to “output” a signal to a signal receiving circuit when the signal driving circuit asserts (or deasserts, if explicitly stated or indicated by context) the signal on a signal line coupled between the signal driving and signal receiving circuits. A signal line is said to be “activated” when a signal is asserted on the signal line, and “deactivated” when the signal is deasserted. Additionally, the prefix symbol “I” attached to signal names indicates that the signal is an active low signal (i.e., the asserted state is a logic low state). A line over a signal name (e.g., ‘ &lt;signal name&gt; ’) is also used to indicate an active low signal. The term “coupled” is used herein to express a direct connection as well as a connection through one or more intervening circuits or structures. Integrated circuit device “programming” may include, for example and without limitation, loading a control value into a register or other storage circuit within the device in response to a host instruction and thus controlling an operational aspect of the device, establishing a device configuration or controlling an operational aspect of the device through a one-time programming operation (e.g., blowing fuses within a configuration circuit during device production), and/or connecting one or more selected pins or other contact structures of the device to reference voltage lines (also referred to as strapping) to establish a particular device configuration or operation aspect of the device. “AC-coupled” or “AC-coupling” refers to a capacitive or inductive interconnection between two nodes. An AC-coupled transmitter refers to a signal transmission circuit having a signal driver and an AC coupling between the signal driver and an output node of the AC-coupled transmitter. The term “exemplary” is used to express an example, not a preference or requirement. 
     While the invention has been described with reference to specific embodiments thereof, it will be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, features or aspects of any of the embodiments may be applied, at least where practicable, in combination with any other of the embodiments or in place of counterpart features or aspects thereof. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.