High-speed controller for phase-change memory peripheral device
First Claim
1. A serializing token-stub phase-change memory (PCM) comprising:
- an upstream serial interface to a memory controller or to an upstream phase-change memory device in a token-stub of phase-change memory devices;
a downstream serial interface to a downstream phase-change memory device in the token-stub of phase-change memory devices;
a deserializer that extracts a write address and a write word in a write request from a serial bitstream received by the upstream serial interface when the write address is within an address range of the serializing token-stub phase-change memory;
wherein the deserializer further extracts a read address in a read request from the serial bitstream received by the upstream serial interface when the read address is within the address range of the serializing token-stub phase-change memory;
a serializer that generates a serial output bitstream to the upstream serial interface from a read data word in response to the read request;
a host write buffer, coupled to the deserializer, for storing a write data word;
a host read buffer, coupled to the serializer, for storing the read data word;
a plurality of PCM cells each having a first logical state having an alloy in a crystalline phase and a second logical state having the alloy in an amorphous phase, wherein a resistance of the alloy is higher when in the amorphous phase than when in the crystalline phase;
a plurality of banks, each bank comprising;
an array of the plurality of PCM cells;
a row decoder, receiving a row portion of the write address or receiving a row portion of the read address, for selecting a row of the plurality of PCM cells selected by an activated word line selected from a plurality of word lines in the array;
a column decoder, receiving a column portion of the write address or receiving a column portion of the read address, for selecting a column of the plurality of PCM cells in the array as selected PCM cells;
local sense amplifiers for reading the read data word stored in the selected PCM cells in response to the read address; and
local write drivers activated by the write data word for driving a set pulse for a set period of time to the selected PCM cells that are being written to a first logical state, and for driving a reset pulse for a reset period of time to the selected PCM cells that are being written to a second logical state;
whereby set and reset pulses are driven to the selected PCM cells from the write data word received by the upstream serial interface.
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Abstract
Phase-change memory (PCM) cells store data using alloy resistors in high-resistance amorphous and low-resistance crystalline states. The time of the memory cell'"'"'s set-current pulse can be 100 ns, much longer than read or reset times. The write time depends on the write data state and is relatively long for set, but short for clear. A PCM chip has a lookup table (LUT) caching write data that is later written to a PCM bank. Host data is latched into a line FIFO and written into the LUT, reducing write delays to the slower PCM. The PCM chip has upstream and downstream serial interfaces to other PCM chips arranged as a token stub. Requests are passed down the token-stub while acknowledgements are passed up the token-stub to the host'"'"'s memory controller. Shared chip-enable lines are driven by the upstream PCM chip for requests, and by the downstream PCM chip for acknowledgements.
85 Citations
20 Claims
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1. A serializing token-stub phase-change memory (PCM) comprising:
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an upstream serial interface to a memory controller or to an upstream phase-change memory device in a token-stub of phase-change memory devices; a downstream serial interface to a downstream phase-change memory device in the token-stub of phase-change memory devices; a deserializer that extracts a write address and a write word in a write request from a serial bitstream received by the upstream serial interface when the write address is within an address range of the serializing token-stub phase-change memory; wherein the deserializer further extracts a read address in a read request from the serial bitstream received by the upstream serial interface when the read address is within the address range of the serializing token-stub phase-change memory; a serializer that generates a serial output bitstream to the upstream serial interface from a read data word in response to the read request; a host write buffer, coupled to the deserializer, for storing a write data word; a host read buffer, coupled to the serializer, for storing the read data word; a plurality of PCM cells each having a first logical state having an alloy in a crystalline phase and a second logical state having the alloy in an amorphous phase, wherein a resistance of the alloy is higher when in the amorphous phase than when in the crystalline phase; a plurality of banks, each bank comprising; an array of the plurality of PCM cells; a row decoder, receiving a row portion of the write address or receiving a row portion of the read address, for selecting a row of the plurality of PCM cells selected by an activated word line selected from a plurality of word lines in the array; a column decoder, receiving a column portion of the write address or receiving a column portion of the read address, for selecting a column of the plurality of PCM cells in the array as selected PCM cells; local sense amplifiers for reading the read data word stored in the selected PCM cells in response to the read address; and local write drivers activated by the write data word for driving a set pulse for a set period of time to the selected PCM cells that are being written to a first logical state, and for driving a reset pulse for a reset period of time to the selected PCM cells that are being written to a second logical state; whereby set and reset pulses are driven to the selected PCM cells from the write data word received by the upstream serial interface. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
whereby set and reset pulses are driven to the selected PCM cells from the write data word initially stored in the cache, freeing the write data lines for other data transfers when the set and reset pulses are applied.
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4. The serializing token-stub phase-change memory of claim 3 further comprising:
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a handshake protocol controller for delaying generation of the upstream acknowledgement signal by the upstream serial interface when the read data word is not stored in the cache, whereby non-cached data delays generation of the upstream acknowledgement signal.
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5. The serializing token-stub phase-change memory of claim 3 further comprising:
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an upstream shared chip-enable line, coupled between the upstream serial interface and the upstream phase-change memory device in the token-stub, wherein the upstream serial interface drives the upstream shared chip-enable line when sending an acknowledgement serial bitstream; and a downstream shared chip-enable line, coupled between the downstream serial interface and the downstream phase-change memory device in the token-stub, wherein the downstream serial interface drives the downstream shared chip-enable line when sending the serial bitstream.
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6. The serializing token-stub phase-change memory of claim 3 wherein a PCM cell in the plurality of PCM cells comprises:
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a select transistor receiving a word line on a gate, and having a channel between a bit line and a cell node; an alloy resistor formed from the alloy, coupled between the cell node and an array voltage; wherein the PCM cell has the first logical state when the alloy resistor has the alloy in the crystalline phase, the alloy resistor having a low resistance that increases a sensing current from the bit line through the select transistor; wherein the PCM cell has the second logical state when the alloy resistor has the alloy in the amorphous phase, the alloy resistor having a high resistance that reduces the sensing current from the bit line through the select transistor; wherein the high resistance is larger than the low resistance; whereby the sensing current is altered by the alloy being in the crystalline phase and the amorphous phase.
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7. The serializing token-stub phase-change memory of claim 6 wherein the alloy is a chalcogenide glass layer having a melting point that is higher than a crystallization point.
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8. The serializing token-stub phase-change memory of claim 7 wherein the alloy is an alloy of germanium (Ge), antimony (Sb), and tellurium (Te).
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9. A memory system comprising:
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phase-change memory means for storing a data word as binary bits each represented by a chalcogenide glass layer having a melting point that is higher than a crystallization point, the chalcogenide glass layer forming a variable resistor that alters a sensing current when a binary bit is read; wherein a crystalline state of the variable resistor represents a first binary logic state and an amorphous state of the variable resistor represents a second binary logic state for binary bits stored in the phase-change memory means; upstream serial interface means for receiving a request from a host in response to a write request from the host, and for outputting an acknowledgement to the host in response to a read request from the host; downstream serial interface means for sending the request from the host to a downstream phase-change-memory chip when the request contains an address that is not within an address range of the phase-change memory means, and for receiving a downstream acknowledgement to the host from the downstream phase-change-memory chip, and for passing the downstream acknowledgement to the upstream serial interface means for transmission toward the host; de-serializing means for extracting a data I/O word from a serial bitstream containing the request received by the upstream serial interface means; serializing means for generating an acknowledgement serial bitstream to the upstream serial interface means for transmission with the acknowledgement, the acknowledgement serial bitstream being generated from a data I/O word read from the phase-change memory means in response to a read request from the host; and I/O buffer means for storing the data I/O word received from the host by the upstream serial interface means until a data word is accumulated, whereby requests and acknowledgements are sent over upstream and downstream serial interfaces with data I/O words stored by the phase-change memory means. - View Dependent Claims (10, 11, 12)
whereby host write data is stored in the lookup table means before writing to the phase-change memory means in the bank means.
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11. The memory system of claim 10 wherein each bank means further comprises:
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set current timer means, coupled to the bank write means, for applying a set current for a set period of time to the selected cells to set variable resistors into the crystalline state when the binary bits being written are in the first binary logic state; reset current timer means, coupled to the bank write means, for applying a reset current for a reset period of time to the selected cells to reset variable resistors into the amorphous state when the binary bits being written are in the second binary logic state; wherein the reset current is at least twice the set current, and wherein the set current is at least twice a sensing current that passes through the variable resistor during a read operation; wherein the set period of time is at least double the reset period of time, whereby the variable resistor is set by a lower current for a longer time period, and reset by a higher current and a shorter time period.
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12. The memory system of claim 11 further comprising:
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error correction means, coupled to the lookup table means, for generating error-correction code for data I/O words stored in the lookup table means, and for checking and correcting errors in data I/O words read from the phase-change memory means and stored in the lookup table means using error-correction code stored in the phase-change memory means, whereby error correction is performed for data in the lookup table means.
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13. A serial token-interface phase-change memory device comprising:
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an upstream serial interface that externally connects to a memory controller or to another serial token-interface phase-change memory device in a token-stub of serial token-interface phase-change memory devices that connect to the memory controller; a downstream serial interface that externally connects to another serial token-interface phase-change memory device in the token-stub of serial token-interface phase-change memory devices; a serial-parallel converter, coupled to the upstream serial interface, for generating a parallel bitstream from a serial bitstream received by the upstream serial interface, and for generating serial data for transmission by the upstream serial interface from a parallel read data word; an address-data mux, coupled to the serial-parallel converter, for generating a parallel address and a parallel write data word from the parallel bitstream from the serial-parallel converter; a plurality of banks of memory cells, each bank in the plurality of banks having an array of memory cells; an alloy resistor in each memory cell in each array of memory cells, the alloy resistor storing binary data as solid phases each having a different resistivity; wherein the alloy resistor changes from a crystalline state to an amorphous state when a memory cell is written from a logic 1 state to a logic 0 state in response to a reset current for a reset period of time; wherein the alloy resistor changes from the amorphous state to the crystalline state when the memory cell is written from a logic 0 state to a logic 1 state in response to a set current for a set period of time; wherein the amorphous state has a higher resistance than the crystalline state that is sensed by a sense amplifier; a data input for receiving the parallel write data word from the address-data mux; and a write input buffer, coupled to the data input to receive the parallel write data word, wherein the parallel write data word converted from the serial bitstream is written to the alloy resistors in memory cells. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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Specification