Integrated circuit having a switch

A reprogrammable switch includes first phase-change material, a reference element, and a sense amplifier. The sense amplifier is coupled to the first phase-change material and the reference element and configured to compare a signal from the first phase-change material to a signal from the reference element and output a voltage signal based on the comparison.

BACKGROUND

Phase-change materials exhibit at least two different states. The states of phase-change material may be referenced to as amorphous and crystalline states. The states may be distinguished because the amorphous state generally exhibits higher resistivity than does the crystalline state. Generally, the amorphous state involves a more disordered atomic structure, while the crystalline state is an ordered lattice. Some phase-change materials exhibit two crystalline states, e.g. a face-centered cubic (FCC) state and a hexagonal closest packing (HCP) state. These two crystalline states have different resistivities. In the following description, the amorphous state generally refers to the state having the higher resistivity, and the crystalline state generally refers to the state having the lower resistivity.

Phase change in the phase-change materials may be induced reversibly. In this way, the phase-change material may change from the amorphous state to the crystalline state, and from the crystalline state to the amorphous state, in response to temperature changes. The temperature changes to the phase-change material may be achieved in a variety of ways. For example, a laser can be directed to the phase-change material, current may be driven through the phase-change material, or current can be fed through a resistive heater adjacent the phase-change material. With any of these methods, controllable heating of the phase-change material causes controllable phase change within the phase-change material.

Typically, semiconductor chips, such as memories, use fuses to configure the chip or deactivate failing portions of the chip. There are two types of fuses, laser fuses and e-fuses. Laser fuses are opened with a laser and e-fuses are opened with an electrical pulse. Alternatively, electrical antifuses can be used in place of fuses. Antifuses break down a thin dielectric to provide a current path. These solutions use a significant amount of chip space and are therefore costly to implement. Laser fuses are limited by the laser focus spot size and e-fuses and antifuses are limited by minimum size requirements for reliable operation. In addition, these fuses and antifuses are only one time programmable (OTP).

SUMMARY

One embodiment of the present invention provides a reprogrammable switch. The reprogrammable switch includes first phase-change material, a reference element, and a sense amplifier. The sense amplifier is coupled to the first phase-change material and the reference element and configured to compare a signal from the first phase-change material to a signal from the reference element and output a voltage signal based on the comparison.

DETAILED DESCRIPTION

FIG. 1illustrates a block diagram of one embodiment of a device100including reprogrammable phase-change material switches. Device100includes a write pulse generator102, a distribution circuit104, reprogrammable switches106a,106b,106c, and106d, and optional reference phase-change element110. In one embodiment, reprogrammable switches106a-106dare phase-change material switches that are based on the amorphous to crystalline phase transition of the phase-change material.

Each reprogrammable switch106a-106dincludes phase-change material. The reprogrammable switches106a-106dcan also be used in place of fuses or antifuses to configure or deactivate part of a chip. The amorphous or crystalline state of the phase-change material of each reprogrammable switch106a-106ddetermines whether the switch is open (not conducting) or closed (conducting). In one embodiment, a comparison of the resistance of the phase-change material in each reprogrammable switch106a-106dwith the resistance of reference phase-change element110determines whether the switch is open or closed.

In one embodiment, write pulse generator102is an internal write pulse generator that is part of the same chip as distribution circuit104and reprogrammable switches106a-106d. In this embodiment, reprogrammable switches106a-106dcan be programmed by write pulse generator102at any time throughout the life of the device. In another embodiment, write pulse generator102is an external write pulse generator that is not part of the same chip as distribution circuit104and reprogrammable switches106a-106d. In this embodiment, an external write pulse generator102is temporarily coupled to distribution circuit104to program reprogrammable switches106a-106d. This allows for programming or configuration of the chip during manufacturing that cannot be changed later by the user. Such one-time programming can be used for additional security features such as serial numbers, encryption codes, etc.

In one embodiment, write pulse generator102generates current or voltage pulses that are controllably directed to reprogrammable phase-change material switches106a-106dvia distribution circuit104to program the reprogrammable phase-change material switches106a-106d. In one embodiment, distribution circuit104includes a plurality of transistors that controllably direct current or voltage pulses to the reprogrammable phase-change material switches through signal paths108a-108dand to optional reference phase-change element110through signal path112.

In one embodiment, reprogrammable switches106a-106dand optional reference phase-change element110include phase-change material that may be changed from an amorphous state to a crystalline state or from a crystalline state to an amorphous state under influence of temperature change. The degree of crystallinity thereby defines at least two states for opening or closing the switch within device100. The at least two states can be assigned to the switch “off” and switch “on” states or the fuse “open” and fuse “closed” states. The switch “off” and “on” states or the fuse “open” and “closed” states of reprogrammable phase-change material switches106a-106ddiffer significantly in their electrical resistivity. In the amorphous state, a phase-change material exhibits significantly higher resistivity than in the crystalline state.

To program a reprogrammable phase-change material switch106a-106dwithin device100, write pulse generator102generates a current or voltage pulse for heating the phase-change material in the target reprogrammable phase-change material switch. In one embodiment, write pulse generator102generates an appropriate current or voltage pulse, which is fed into distribution circuit104and distributed to the appropriate target reprogrammable phase-change material switch106a-106dthrough signal path108a-108d. The current or voltage pulse amplitude and duration is controlled depending on whether the reprogrammable phase-change material switch is being turned on or off. Generally, a “set” operation of a reprogrammable phase-change material switch is heating the phase-change material of the target reprogrammable phase-change material switch above its crystallization temperature (but below its melting temperature) long enough to achieve the crystalline state. Generally, a “reset” operation of a reprogrammable phase-change material switch is heating the phase-change material of the target reprogrammable phase-change material switch above its melting temperature, and then quickly quench cooling the phase-change material, thereby achieving the amorphous state. Reference phase-change element110is set and reset similarly to reprogrammable switches106a-106dthrough signal path112.

FIG. 2illustrates one embodiment of a reprogrammable phase-change material switch150a. Reprogrammable phase-change material switch150aincludes first contact112, first phase-change material114, second contact116, third contact140, second phase-change material142, fourth contact144, and a sense amplifier (SA)154. First contact112receives a constant voltage (V+) or one side of a write pulse (WP+) signal on V+/WP+ signal path138a. First contact112is electrically coupled to first phase-change material114. First phase-change material114is electrically coupled to second contact116. Second contact116is electrically coupled to an input of sense amplifier154through the other side of the write pulse (WP−) signal path138b. Third contact140receives a constant voltage (V+) or one side of a write pulse (WP+) signal on V+/WP+ signal path138c. Third contact140is electrically coupled to second phase-change material142. Second phase-change material142is electrically coupled to fourth contact144. Fourth contact144is electrically coupled to another input of sense amplifier154through the other side of the write pulse (WP−) signal path152. Sense amplifier154provides the out (OUT) signal on OUT signal path156.

First phase-change material114and second phase-change material142may be made up of a variety of materials in accordance with the present invention. Generally, chalcogenide alloys that contain one or more elements from group VI of the periodic table are useful as such materials. In one embodiment, first phase-change material114and second phase-change material142of reprogrammable phase-change material switch150aare made up of a chalcogenide compound material, such as GeSbTe, SbTe, or AgInSbTe. In another embodiment, the phase-change material can be chalcogen free, such as GeSb, GaSb, or GeGaSb.

During programming of first phase-change material114of reprogrammable phase-change material switch150a,write pulse generator102is selectively coupled across first contact112and second contact116. Write pulse generator102controls the application of a current and/or voltage write pulse from first contact112through V+/WP+ signal path138ato second contact116through WP− signal path138b, and thus to first phase-change material114, to set or reset first phase-change material114. During a set operation of first phase-change material114, a set current and/or voltage pulse is selectively enabled by write pulse generator102and sent through first contact112to first phase-change material114thereby heating first phase-change material114above its crystallization temperature (but usually below its melting temperature). In this way, first phase-change material114reaches its crystalline state during this set operation. During a reset operation of first phase-change material114, a reset current and/or voltage pulse is selectively enabled by write pulse generator102and sent through first contact112to first phase-change material114. The reset current or voltage quickly heats first phase-change material114above its melting temperature. After the current and/or voltage pulse is turned off, first phase-change material114quickly quench cools into the amorphous state.

During programming of second phase-change material142of reprogrammable phase-change material switch150a, write pulse generator102is selectively coupled across third contact140and fourth contact144. Write pulse generator102controls the application of a current and/or voltage write pulse from third contact140through V+/WP+ signal path138cto fourth contact144through WP− signal path152, and thus to second phase-change material142, to set or reset second phase-change material142. During a set operation of second phase-change material142, a set current and/or voltage pulse is selectively enabled by write pulse generator102and sent through third contact140to second phase-change material142thereby heating second phase-change material142above its crystallization temperature (but usually below its melting temperature). In this way, second phase-change material142reaches its crystalline state during this set operation. During a reset operation of second phase-change material142, a reset current and/or voltage pulse is selectively enabled by write pulse generator102and sent through third contact140to second phase-change material142. The reset current or voltage quickly heats second phase-change material142above its melting temperature. After the current and/or voltage pulse is turned off, second phase-change material142quickly quench cools into the amorphous state.

In one embodiment, second phase-change material142provides a fixed reference, such as reference phase-change element110, to compare to first phase-change material114. In one embodiment, second phase-change material142is programmed once at device fabrication. In one embodiment, second phase-change material142provides a fixed reference for more than one reprogrammable phase-change material switch150a. During operation of reprogrammable phase-change material switch150a, the constant voltage V+ is selectively applied to first contact112through V+/WP+ signal path138aand the constant voltage V+ is applied to third contact140through V+/WP+ signal path138c. With the constant voltage V+ applied to first contact112and the constant voltage V+ applied to third contact140, sense amplifier154compares the current on signal path152to the current on signal path138b. If first phase-change material114is in the amorphous state and second phase-change material142is in the crystalline state, or if the resistance of first phase-change material114is significantly greater than the resistance of second phase-change material142, then the current through first phase-change material114is small compared to the current through second phase-change material142. Therefore, the current on signal path138bis less than the current on signal path152. In response to the current on signal path138bbeing less than the current on signal path152, sense amplifier154outputs a high voltage level signal on OUT signal path156turning on reprogrammable phase-change material switch150a.

If first phase-change material114is in the crystalline state and second phase-change material142is in the amorphous state, or if the resistance of first phase-change material114is significantly less than the resistance of second phase-change material142, then the current through first phase-change material114is large compared to the current through second phase-change material142. Therefore, the current on signal path138bis greater than the current on signal path152. In response to the current on signal path138bbeing greater than the current on signal path152, sense amplifier154outputs a low voltage level signal or ground signal on OUT signal path156turning off reprogrammable phase-change material switch150a. In another embodiment, the voltage levels output by sense amplifier154based on the states of first phase-change material114and second phase-change material142are reversed.

FIG. 3illustrates another embodiment of a reprogrammable phase-change material switch150b. Reprogrammable phase-change material switch150bis similar to reprogrammable phase-change material switch150aexcept third contact140, second phase-change material142, and fourth contact144are replaced by resistor120, which is a reference element. Resistor120receives the constant voltage (V+) on V+ signal path138c. Resistor120is electrically coupled to an input of sense amplifier154through signal path152. First contact112receives the constant voltage (V+) or one side of a write pulse (WP+) signal on V+/WP+ signal path138a. First contact112is electrically coupled to phase-change material114. Phase-change material114is electrically coupled to second contact116. Second contact116is electrically coupled to another input of sense amplifier154through the other side of the write pulse (WP−) signal path138b.

During programming of phase-change material114of reprogrammable phase-change material switch150b, write pulse generator102is selectively coupled across first contact112and second contact116. Write pulse generator102controls the application of a current and/or voltage write pulse from first contact112through V+/WP+ signal path138ato second contact116through WP− signal path138b, and thus to phase-change material114, to set or reset phase-change material114. During a set operation of phase-change material114, a set current and/or voltage pulse is selectively enabled by write pulse generator102and sent through first contact112to phase-change material114thereby heating phase-change material114above its crystallization temperature (but usually below its melting temperature). In this way, phase-change material114reaches its crystalline state during this set operation. During a reset operation of phase-change material114, a reset current and/or voltage pulse is selectively enabled by write pulse generator102and sent through first contact112to phase-change material114. The reset current or voltage quickly heats phase-change material114above its melting temperature. After the current and/or voltage pulse is turned off, phase-change material114quickly quench cools into the amorphous state.

In one embodiment, resistor120provides a fixed reference to compare to phase-change material114. In one embodiment, resistor120provides a fixed reference for more than one reprogrammable phase-change material switch150b. During operation of reprogrammable phase-change material switch150b, the constant voltage V+ is selectively applied to first contact112through V+/WP+ signal path138aand the constant voltage V+ is applied to resistor120through V+ signal path138c. With the constant voltage V+ applied to first contact112and the constant voltage V+ applied to resistor120, sense amplifier154compares the current on signal path152to the current on signal path138b. If phase-change material114is in the crystalline state, or if the resistance of phase-change material114is significantly less than the resistance of resistor120, then the current through phase-change material114is large compared to the current through resistor120. Therefore, the current on signal path138bis greater than the current on signal path152. In response to the current on signal path138bbeing greater than the current on signal path152, sense amplifier154outputs a high voltage level signal on OUT signal path156turning on reprogrammable phase-change material switch150b.

If phase-change material114is in the amorphous state, or if the resistance of phase-change material114is significantly greater than the resistance of resistor120, then the current through phase-change material114is small compared to the current through resistor120. Therefore, the current on signal path138bis less than the current on signal path152. In response to the current on signal path138bbeing less than the current on signal path152, sense amplifier154outputs a low voltage level signal or ground signal on OUT signal path156turning off reprogrammable phase-change material switch150b. In another embodiment, the voltage levels output by sense amplifier154based on the state of phase-change material114and the resistance of resistor120are reversed.

FIG. 4illustrates another embodiment of a reprogrammable phase-change material switch160a. Reprogrammable phase-change material switch160aincludes first contact112, first phase-change material114, second contact116, third contact140, second phase-change material142, fourth contact144, resistor162, resistor168, and a sense amplifier (SA)154. In one embodiment, the resistance of resistor162is approximately equal to the resistance of resistor168. First contact112receives a constant voltage (V+) or one side of a write pulse (WP+) signal on V+/WP+ signal path138a. First contact112is electrically coupled to first phase-change material114. First phase-change material114is electrically coupled to second contact116. Second contact116is electrically coupled to an input of sense amplifier154and one side of resistor168through the other side of the write pulse (WP−) signal path138b. The other side of resistor168is electrically coupled to common or ground164through signal path170. Third contact140receives a constant voltage (V+) or one side of a write pulse (WP+) signal on V+/WP+ signal path138c. Third contact140is electrically coupled to second phase-change material142. Second phase-change material142is electrically coupled to fourth contact144. Fourth contact144is electrically coupled to another input of sense amplifier154and one side of resistor162through the other side of write pulse (WP−) signal path152. The other side of resistor162is electrically coupled to common or ground164through signal path166. Sense amplifier154provides the out (OUT) signal on OUT signal path156.

During programming of first phase-change material114of reprogrammable phase-change material switch160a, write pulse generator102is selectively coupled across first contact112and second contact116. Write pulse generator102controls the application of a current and/or voltage write pulse from first contact112through V+/WP+ signal path138ato second contact116through WP− signal path138b, and thus to first phase-change material114, to set or reset first phase-change material114. During a set operation of first phase-change material114, a set current and/or voltage pulse is selectively enabled by write pulse generator102and sent through first contact112to first phase-change material114thereby heating first phase-change material114above its crystallization temperature (but usually below its melting temperature). In this way, first phase-change material114reaches its crystalline state during this set operation. During a reset operation of first phase-change material114, a reset current and/or voltage pulse is selectively enabled by write pulse generator102and sent through first contact112to first phase-change material114. The reset current or voltage quickly heats first phase-change material114above its melting temperature. After the current and/or voltage pulse is turned off, first phase-change material114quickly quench cools into the amorphous state.

During programming of second phase-change material142of reprogrammable phase-change material switch160a,write pulse generator102is selectively coupled across third contact140and fourth contact144. Write pulse generator102controls the application of a current and/or voltage write pulse from third contact140through V+/WP+ signal path138cto fourth contact144through WP− signal path152, and thus to second phase-change material142, to set or reset second phase-change material142. During a set operation of second phase-change material142, a set current and/or voltage pulse is selectively enabled by write pulse generator102and sent through third contact140to second phase-change material142thereby heating second phase-change material142above its crystallization temperature (but usually below its melting temperature). In this way, second phase-change material142reaches its crystalline state during this set operation. During a reset operation of second phase-change material142, a reset current and/or voltage pulse is selectively enabled by write pulse generator102and sent through third contact140to second phase-change material142. The reset current or voltage quickly heats second phase-change material142above its melting temperature. After the current and/or voltage pulse is turned off, second phase-change material142quickly quench cools into the amorphous state.

In one embodiment, second phase-change material142provides a fixed reference, such as reference phase-change element110, to compare to first phase-change material114. In one embodiment, second phase-change material142is programmed once at device fabrication. In one embodiment, second phase-change material142provides a fixed reference for more than one reprogrammable phase-change material switch160a. During operation of reprogrammable phase-change material switch160a, the constant voltage V+ is selectively applied to first contact112through V+/WP+ signal path138aand the constant voltage V+ is applied to third contact140through V+/WP+ signal path138c. With the constant voltage V+ applied to first contact112, a voltage divider is formed by first phase-change material114and resistor168. With the constant voltage V+ applied to third contact140, a voltage divider is formed by second phase-change material142and resistor162. Sense amplifier154compares the voltage on signal path152to the voltage on signal path138b. If first phase-change material114is in the amorphous state and second phase-change material142is in the crystalline state, or if the resistance of first phase-change material114is significantly greater than the resistance of second phase-change material142, then the voltage drop across first phase-change material114is large compared to the voltage drop across second phase-change material142. Therefore, the voltage on signal path138bis less than the voltage on signal path152. In response to the voltage on signal path138bbeing less than the voltage on signal path152, sense amplifier154outputs a high voltage level signal on OUT signal path156turning on reprogrammable phase-change material switch160a.

If first phase-change material114is in the crystalline state and second phase-change material142is in the amorphous state, or if the resistance of first phase-change material114is significantly less than the resistance of second phase-change material142, then the voltage drop across first phase-change material114is small compared to the voltage drop across second phase-change material142. Therefore, the voltage on signal path138bis greater than the voltage on signal path152. In response to the voltage on signal path138bbeing greater than the voltage on signal path152, sense amplifier154outputs a low voltage level signal or ground signal on OUT signal path156turning off reprogrammable phase-change material switch160a. In another embodiment, the voltage levels output by sense amplifier154based on the states of first phase-change material114and second phase-change material142are reversed.

FIG. 5illustrates another embodiment of a reprogrammable phase-change material switch160b. Reprogrammable phase-change material switch160bis similar to reprogrammable phase-change material switch160aexcept third contact140, second phase-change material142, fourth contact144, and resistor162are removed. An input of sense amplifier154receives the constant voltage (V+) on V+ signal path138c. First contact112receives the constant voltage (V+) or one side of a write pulse (WP+) signal on V+/WP+ signal path138a. First contact112is electrically coupled to phase-change material114. Phase-change material114is electrically coupled to second contact116. Second contact116is electrically coupled to another input of sense amplifier154and one side of resistor168through the other side of the write pulse (WP−) signal path138b. The other side of resistor168is electrically coupled to common or ground164through signal path170.

During programming of phase-change material114of reprogrammable phase-change material switch160b, write pulse generator102is selectively coupled across first contact112and second contact116. Write pulse generator102controls the application of a current and/or voltage write pulse from first contact112through V+/WP+ signal path138ato second contact116through WP− signal path138b, and thus to phase-change material114, to set or reset phase-change material114. During a set operation of phase-change material114, a set current and/or voltage pulse is selectively enabled by write pulse generator102and sent through first contact112to phase-change material114thereby heating phase-change material114above its crystallization temperature (but usually below its melting temperature). In this way, phase-change material114reaches its crystalline state during this set operation. During a reset operation of phase-change material114, a reset current and/or voltage pulse is selectively enabled by write pulse generator102and sent through first contact112to phase-change material114. The reset current or voltage quickly heats phase-change material114above its melting temperature. After the current and/or voltage pulse is turned off, phase-change material114quickly quench cools into the amorphous state.

The constant voltage V+ on signal path138cprovides a fixed reference voltage to compare to the voltage drop across phase-change material114. During operation of reprogrammable phase-change material switch160b, the constant voltage V+ is selectively applied to first contact112through V+/WP+ signal path138aand the constant voltage V+ is applied to an input of sense amplifier154through signal path138c. With the constant voltage V+ applied to first contact112, a voltage divider is formed by first phase-change material114and resistor168. With the constant voltage V+ applied to an input of sense amplifier154, sense amplifier154compares the voltage on signal path138cto the voltage on signal path138b. If phase-change material114is in the crystalline state, then the voltage drop across phase-change material114is small. Therefore, the voltage on signal path138bis approximately equal to the voltage on signal path138c. In response to the voltage on signal path138bbeing approximately equal to the voltage on signal path138c, sense amplifier154outputs a high voltage level signal on OUT signal path156turning on reprogrammable phase-change material switch160b.

If phase-change material114is in the amorphous state, then the voltage drop across phase-change material114is large. Therefore, the voltage on signal path138bis less than the voltage on signal path138c. In response to the voltage on signal path138bbeing less than the voltage on signal path138c, sense amplifier154outputs a low voltage level signal or ground signal on OUT signal path156turning off reprogrammable phase-change material switch160b. In another embodiment, the voltage levels output by sense amplifier154based on the state of phase-change material114are reversed.

Embodiments of the present invention provide a reprogrammable switch, which can also be used as a fuse or antifuse using phase-change material. The resistivity of the phase-change material determines whether the switch is on or off or if used as a fuse or antifuse, whether the fuse or antifuse is open or closed. The switches are reprogrammable and use a small amount of space on a semiconductor chip compared to laser fuses and e-fuses. In addition, for phase-change memories, the reprogrammable switches can be fabricated simultaneously with the memory cells further reducing the cost.