Thin film device and a method of providing thermal assistance therein

A thin film device and a method of providing thermal assistance therein is disclosed. Accordingly, a heater material is utilized to thermally assist in the operation of the thin film device. By utilizing a heater material to thermally assist in the operation of the thin film device, a substantial improvement in the accuracy and performance of the thin film device is achieved. A first aspect of the present invention is a thin film device. The thin film device includes at least one patterned thin film layer, a heater material coupled to the at least one patterned thin film layer for providing thermal assistance to the at least one of the patterned thin film layers and a conductor coupled to the heater material for supplying energy to the heater material.

FIELD OF THE INVENTION

The present invention relates generally to thin film devices and more particularly to a thin film device and a method of providing thermal assistance therein.

BACKGROUND OF THE INVENTION

Thin film devices comprising device layers deposited on CMOS substrates are well-known. Such a thin film device is manufactured by stacking a plurality of device layers in order on a substrate. Such devices include memory elements, sensors, emitters, etc.

Consider the example of an MRAM thin film device including a resistive cross point array of spin dependent tunneling (SDT) junctions, word lines extending along rows of the SDT junctions, and bit lines extending along columns of the SDT junctions. Each SDT junction is located at a cross point of a word line and a bit line. The magnetization of each SDT junction assumes one of two stable orientations at any given time. These two stable orientations, parallel and anti-parallel, represent logic values of ‘0’ and ‘1’. The magnetization orientation, in turn, affects the resistance of the SDT junction. Resistance of the SDT junction is a first value (R) if the magnetization orientation is parallel and a second value (R+ΔR) if the magnetization orientation is anti-parallel. The magnetization orientation of the SDT junction and, therefore, its logic value may be read by sensing its resistance state.

A write operation on a selected SDT junction is performed by supplying write currents to the word and bit lines crossing the selected SDT junction. The currents create two external magnetic fields that, when combined, switch the magnetization orientation of the selected SDT junction from parallel to anti-parallel or vice versa.

Too small a write current might not cause the selected SDT junction to change its magnetization orientation. Conventional MRAM designs sometimes need one or two current driven magnetic fields to switch the magnetization orientation. However, the magnitude of the current(s) needed to switch the magnetization orientation is too high to maintain the cost advantage of the implementation of the MRAM device. Furthermore, as technology develops, this problem will be exacerbated.

Accordingly, what is needed is a thin film device and a method of implementation thereof that addresses the above described problem related to MRAM devices. The present invention addresses this need.

SUMMARY OF THE INVENTION

A thin film device and a method of providing thermal assistance therein is disclosed. Accordingly, a heater material is utilized to thermally assist in the operation of the thin film device. By utilizing a heater material to thermally assist in the operation of the thin film device, a substantial improvement in the accuracy and performance of the thin film device is achieved.

A first aspect of the present invention is a thin film device. The thin film device includes at least one patterned thin film layer, a heater material coupled to the at least one patterned thin film layer for providing thermal assistance to the at least one patterned thin film layer and a conductor coupled to the heater material for supplying energy to the heater material.

A second aspect of the present invention is a method of providing thermal assistance in a thin film device. The method includes heating at least one of a plurality of patterned thin film layers by selectively exposing the at least one of the plurality of patterned thin film layers to energy from a power source and performing an operation with the selectively exposed at least one of the plurality of patterned thin films.

DETAILED DESCRIPTION

As shown in the drawings for purposes of illustration, a thin film device and a method of providing thermal assistance therein is disclosed. Accordingly, a heater material is utilized to thermally assist in the operation of the thin film device. By utilizing a heater material to thermally assist in the operation of the thin film device, a substantial improvement in the accuracy and performance of the thin film device is achieved.

FIG. 1is a high level flow chart of a method providing thermal assistance in a thin film device. A first step110includes heating at least one of a plurality of patterned thin film layers by selectively exposing the at least one of the plurality of patterned thin film layers to energy from a power source. A second step120includes performing an operation with the selectively exposed at least one of the plurality of patterned thin films.

The method of providing thermal assistance to a thin film device is a generic method and has applications in many areas. Consider the example of the MRAM thin film device. As shown in the drawings for purposes of illustration, the MRAM device includes a plurality of magnetic memory elements. A magnetic memory element of the MRAM device could be any element having a resistance that is dependent upon the state of its magnetic film. Examples of such elements include magnetic tunnel junctions (the spin dependent tunnel (SDT) junction is a type of magnetic tunnel junction) and giant magnetoresistance (“GMR”) spin valves. For the purposes of illustration, the memory elements will be described below as SDT junctions.

FIG. 2shows an SDT junction200. The SDT junction200includes a patterned group of thin film layers. This group includes a pinned layer212having a magnetization that is oriented in the plane of the pinned layer212but fixed by an anti-ferromagnetic pinning layer (not shown) so as not to rotate in the presence of an applied magnetic field in a range of interest. In an alternate embodiment, the pinned layer212is a synthetic ferromagnet pinned by an anti-ferromagnetic pinning layer.

The SDT junction200also includes a “free” layer214having a magnetization orientation that is not pinned. Rather, the magnetization can be oriented in either of two directions along an axis (the “easy” axis) lying in the plane of the free layer214. Other layers such as seed layers, anti-ferromagnetic pinning layers and synthetic ferromagnetic layers, etc., may also be included in a SDT junction. If the magnetization of the pinned and free layers212and214are in the same direction, the orientation is said to be “parallel” (as indicated by the arrow P). If the magnetization of the pinned and free layers212and214are in opposite directions, the orientation is said to be “anti-parallel” (as indicated by the arrow A). It should also be pointed out that the free layer214is sometimes referred to as the data layer or the sense layer.

The pinned layer212and the free layer214are separated by an insulating tunnel barrier216. Although the free layer214is shown inFIG. 2as being above the tunneling barrier216, the free layer214may be either above or below the tunnel barrier216. The insulating tunnel barrier216allows quantum mechanical tunneling to occur between the pinned layer212and the free layer214. This tunneling phenomenon is electron spin dependent, making the resistance of the SDT junction200a function of the relative orientations of the magnetization of the pinned layer212and the free layer214. For instance, resistance of the SDT junction200is a function of the relative orientations of the magnetization of the pinned layer212and the free layer214. For instance, resistance of the SDT junction200is a first value (R) if the magnetization orientation of the pinned layer212and the free layer214is parallel and a second value (R+ΔR) if the magnetization orientation is anti-parallel.

In an embodiment, the SDT junction200is deposited on a dielectric material230such as SiO2, Si3N4, AlN, Al2O3, etc. The SDT junction200includes a sidewall material222and a heater material224whereby the heater material224is located in between a sidewall material222. The sidewall material222is a highly conductive material capable of absorbing energy from a power source. In an embodiment, the sidewall material222is a material such as Cu, Au, Ag, Pt or any combination thereof. Furthermore, the sidewall material222can be referred to as a “split” conductor since the sidewall material222is split and covers opposite sides of the dielectric material230. Also shown inFIG. 2is an optional dielectric layer226in contact with a sense line220. Otherwise, the heater material224is in direct contact with the sense line220.

Magnetic fields (Hx, Hy) may be applied to the SDT junction200by supplying current (Ix) through the split conductor222and current (Iy) to the conductor218. If the conductors218and222are orthogonal, the applied magnetic fields (Hx, Hy) will also be orthogonal.

When sufficiently large currents (Ix, Iy) are passed through the conductors218and222(e.g. during a write operation), the combined magnetic field (Hx, Hy) in the vicinity of the free layer214causes the magnetization of the free layer214to rotate from the parallel orientation to the anti-parallel orientation, or vice-versa. For example, a sufficient current +Ixwill cause the magnetization to be anti-parallel whereas a sufficient current −Iywill cause the magnetization orientation to be parallel.

Current magnitudes may be selected so that the combined magnetic field (Hx+Hy) exceeds the switching field of the free layer214but does not exceed the switching field of the pinned layer212. However, the magnitude of one or both write currents (Ix, Iy) may be reduced if the SDT junction200is heated. Coercivity of a magnetic film decreases with increasing temperature. Raising the temperature of the SDT junction200reduces the coercivity (Hc) of the SDT junction200as shown inFIGS. 3 and 4.FIG. 3shows the coercivity (Hc) at room temperature whileFIG. 4shows the coercivity (Hc) at a temperature ΔT above room temperature. At the elevated temperature, the SDT junction200switches from a high resistance state to a low resistance state and vice-versa in the presence of a lower combined magnetic field (Hx+Hy). Therefore, heating the SDT junction200allows the magnitudes of one or both of the write currents (Ix, Iy) to be reduced. If, on the other hand, the magnitudes of the write currents (Ix, Iy) are not reduced, the SDT junction200will switch more reliably in the presence of the combined magnetic field (Hx+Hy). The temperature and write current can be varied to achieve a desired switching reliability.

Heat may be applied and removed before the combined magnetic field (Hx+Hy) is applied, or the heat may be applied at the same time as the combined magnetic field (Hx+Hy). The free layer214may be heated to about 0° C. to 50° C. above room temperature. More generally, the maximum heating temperature may be about 50° C. less than the Blocking temperature TB (the temperature above which the pinning properties are lost). However, one of ordinary skill in the art will readily recognize that the free layer214can be heated to any temperature while remaining within the spirit and scope of the present invention.

Heat is applied to the free layer214by connecting a power source to the sidewall material222. In an embodiment, the power source is a high frequency AC power source coupled to a decoder. The frequency can be a radio frequency or any other of a variety of frequencies that are empirically determined. As previously mentioned, a heater material224is located in between the sidewall material222. In varying embodiments, the heater material222is amorphous carbon or amorphous silicon or a metallic material. Accordingly, prior to or simultaneous with the performance of a write operation (i.e. the application of a write current), the power source supplies energy to the sidewall material222.

The energy from the power source is then transferred from the sidewall material222to the heater material224. Accordingly, heat is transferred to the free layer214through the heater material224, the dielectric material226, the sense line220, the pinned layer212and the tunnel barrier216, if the free layer214is above the tunnel barrier216. Alternatively, if the free layer214is below the tunnel barrier216, the heat is transferred to the free layer214through the heater material224, dielectric material226, the sense line220and the pinned layer212. In any case, once heated, the free layer214requires significantly lower write currents to switch the magnetization state.

Please refer now toFIG. 5.FIG. 5is a flow chart illustrating the method steps for fabricating a magnetic random access memory array along with a series of cross sectional views (FIGS. 5(a–g)) showing the resulting structure.

A first step510includes depositing a heater material511over a dielectric material512. The heater material511is metal, amorphous carbon, amorphous silicon or the like. A second step520includes creating trenches521in the dielectric material512. As can be seen inFIG. 5(b), the heater material511remains in between the trenches521. A third step530includes coating the trenches521with a conductive material531. A highly conductive material such as Cu, Au, Ag, Pt or any combination thereof is used in this step.

The next step540includes performing an anisotropic etch on the conductive material531. Since the etching process in step540is anisotropic, meaning that it removes material directionally, this step clears the conductive material531from the tops and bottoms of the trenches521thereby leaving the conductive material531as sidewalls in the trenches521.

A next step550includes depositing a planarizing dielectric551over the structure. A next step560includes etching back the planarizing dielectric551. Here, the planarizing dielectric551is etched back to expose the top of the heater material511. This is accomplished with a chemical-mechanical polishing process or the like. The next step570includes depositing an SDT junction materials stack over the planarized dielectric and heater material511and patterning an SDT junction572wherein the patterned SDT junction572includes a free layer572.

In an embodiment, the conductive sidewall material is coupled to a power source via a decoder whereby the power source is utilized to heat the SDT junction prior to or simultaneous with the application of a write current thereby reducing the amount of current required to switch the magnetization of the free layer.

For a better understanding, please refer now toFIG. 6.FIG. 6is a top perspective view of a structure600in accordance with an embodiment.FIG. 6shows top conductors610, sense lines620and SDT junctions630. The conductive sidewall material640is a material capable of absorbing energy from a power source and is coupled to the decoder650whereby the decoder650is coupled to the power source660. In an embodiment the decoder650applies energy from the power source660to the conductive sidewall material640in a selective fashion. Stated another way, the decoder650selects the row and/or column to which to apply energy from the power source660. The decoder650is coupled to the conductive sidewall material640via copper wire, aluminum wire or the like. In an embodiment, the power source applies radio frequency energy to the sidewall material640.

The MRAM device described herein may be used in a variety of applications.FIG. 7shows an exemplary general application for an MRAM device in accordance with an embodiment. The general application is embodied by a system750including an MRAM device752in accordance with an embodiment, an interface module754and a processor756. Interface module754provides an interface between processor756and MRAM device752. System750could also include other types and/or levels of memory.

For a system750such as a notebook computer or personal computer, the interface module754might include an IDE or SCSI interface. For a system750such as a server, multiple MRAM devices could be implemented and interface module754might include a fiber channel or SCSI interface. For a device750such as a digital camera, the interface module754might include a camera interface. Here, the MRAM device753would allow non-volatile storage of digital images on-board the digital camera.

The above embodiments of the MRAM device may offer advantages over other MRAM devices. For example, a higher level of memory cell densities may be achieved compared to other MRAM devices that include additional elements. Increased densities may result in decreased costs for a given amount of storage capacity. In addition the memory cell strings described herein may provide better electrical circuit isolation compared to previous MRAM devices. The improved isolation may allow for more reliable detection of the state of memory cells in a memory cell string.

The MRAM device may also be used for long-term data storage in a computer. Such a device offers many advantages (e.g. faster speed, smaller size) over hard drives and other conventional long-term data storage devices. Additionally, the MRAM device could possibly replace DRAM and other fast, short-term memory in computers.

The memory device is not limited to the specific embodiments described and illustrated above. For instance, an MRAM device is not limited to the use of spin dependent tunneling devices. Other types of devices that could be used include, but are not limited to, giant magnetoresistance (“GMR”) devices.

Although the above-described embodiments are disclosed in conjunction with the operation of an MRAM device, it should be understood that the above-disclosed to configurations could be implemented in conjunction with a variety of different thin film devices while remaining within the spirit and scope of the present invention. Consider an example of a chemical sensor. So called “Laboratory on a Chip” thin film devices utilize chemical reactions to analyze specimens. The rate of the chemical reactions are exponentially dependent on temperature. Accordingly, by heating the specimen, the rate of the chemical reaction is increased, and the time in which the results are obtained is decreased.

A thin film device and a method of providing thermal assistance therein is disclosed. Accordingly, a heater material is utilized to thermally assist in the operation of the thin film device. By utilizing a heater material to thermally assist in the operation of the thin film device, a substantial improvement in the accuracy and performance of the thin film device is achieved.