Patent Description:
The scaling roadmap of solid-state memory devices is currently dominated by NAND flash. NAND flash is relatively fast and has a small form factor. However, NAND flash is also relatively expensive per stored bit. In addition, the further scaling of NAND flash is becoming increasingly more difficult to achieve and may lead to an increase of its read latency.

Other major memory technologies such as hard disk drives (HDD) and tape memory have a low cost per bit. However, they are much slower than NAND flash and have a large form factor not suitable for integration in handheld devices.

Several alternative memory solutions have been proposed, such as micromechanical probe memory (<NPL>), holographic data storage (<NPL>), or magnetic racetrack memory (<NPL>). However, these memory concepts are currently still at a research level and are not yet commercially available.

In other words, there is still a clear need for a novel commercially viable memory technology with a form factor and speed comparable to NAND flash, but with a higher bit density and lower cost.

<CIT> discloses a storage device using a tape for storing data. The tape includes a plurality of first regions with a lower dielectric constant and a plurality of second regions with a higher dielectric constant, wherein the first regions and the second regions are alternatingly arranged along the length of the tape.

Thus, it is an objective to provide an improved storage device and to provide an improved storage system. In particular, the above-mentioned disadvantages should be avoided.

The objective is achieved by the embodiments provided in the enclosed independent claims. Advantageous implementations of the embodiments of the invention are further defined in the dependent claims.

According to a first aspect, the present disclosure relates to a storage device, comprising a tape configured to store data; a data head configured to read and/or write data from and/or to the tape; an actuator configured to move the tape in a length direction in a step-wise manner, wherein the actuator comprises: a number of pulling electrodes, wherein each pulling electrode is configured to be activated to exert a pulling force on the tape, and a number of clamping electrodes, wherein each clamping electrode is configured to be activated to clamp the tape, the storage device being characterized in that the pulling electrodes and the clamping electrodes are alternately arranged along the length of the tape, the pulling electrodes are arranged at a further distance from the tape than the clamping electrodes, and if activated, each pulling electrode is configured to deform a section of the tape by pulling said section away from a longitudinal axis of the tape, wherein said deformation causes the pulling force on the tape.

This achieves the advantage that a storage device is provided that combines a small form factor, with precise and fast read/write speeds, in particular in terms of latency and throughput. These fast read/write speeds can be achieved due to an actuation mechanism that is based on moving the tape via electrostatic forces.

The tape may be a flexible nanosheet for storing data, for example, a parallel flexible nanosheet storage. A surface area of the tape may be configured to store the data. Such a tape provides a significant area enhancement, i.e., and increased ratio of the storage medium area and the overall storage device area. Thus, such a tape allows building a storage device with a small form factor. Further, the increased ratio reduces the cost per bit of the storage device.

The length of the tape may be varied from millimeters to centimeters.

The actuator can be an electrostatic shuffle tape driver that is configured to move the tape in a step-wise manner. Thereby, tape step frequencies between <NUM> and several MHz can be achieved.

The pulling electrodes and the clamping electrodes may be configured, if activated, to excerpt an attractive electrostatic force on the tape. The actuator can be configured to move the tape in the step-wise manner by activating and deactivating the number of pulling electrodes and clamping electrodes according to a defined activation sequence. Thereby, the pulling electrodes and the clamping electrodes work together to move the tape forward or backward in the length direction. In particular, the pulling electrodes exert the pulling force on the tape which causes the tape movement while the clamping electrodes define the direction of said movement (backwards or forwards).

The actuator can comprise at least three electrodes, namely two clamping electrodes and one pulling electrode. Preferably, the actuator comprises five or more electrodes, for example three clamping electrodes and two pulling electrodes.

In an embodiment, the tape comprises a conductive layer on a bottom side of the tape, which is configured to act as a counter electrode for the pulling electrodes and clamping electrodes, respectively. This achieves the advantage that the tape can be moved efficiently by the actuator based on electrostatic forces.

In an embodiment, the pulling electrodes and the clamping electrodes are arranged below the bottom side of the tape facing the conductive layer.

In particular, the tape exhibits an internal stiffness that additionally supports the movement of the tape. For example, after the pulling electrode is deactivated, the deformed tape reverses the deformation due its internal stiffness, causing an additional pushing force on the tape which supports the tape movement.

In an embodiment, the actuator is configured to move the tape in a first direction by subsequently:.

This achieves the advantage that the tape can be efficiently moved by the actuator.

The above sequence requires a minimum of three electrodes, namely two clamping electrodes and one pulling electrodes. For example, the actuator comprises five electrodes, three clamping and two pulling electrodes, and the above sequence is expanded taking into account the additional electrodes.

In an embodiment, the actuator is configured to activate each clamping electrode by applying a clamping voltage to the clamping electrode, and the actuator is configured to activate each pulling electrode by applying a pulling voltage to the pulling electrode.

In an embodiment, the actuator is configured to control a movement speed of the tape by adjusting the pulling voltage and/or by adjusting an activation frequency of the pulling electrodes and clamping electrodes, respectively. This achieves the advantage that the tape can be moved quickly and precisely depending on a current requirement.

For example, the storage device can be set to a fine stepping mode, which is defined by a pulling voltage that is smaller than a threshold value. In this fine stepping mode, the step size of the tape movement is reduced allowing for nanometer resolution position control with respect to the data head. Alternatively, the storage device can be set to a fast stepping mode, which is defined by a pulling voltage that is larger than the threshold value. In the fast stepping mode the movement speed of the tape is increased, e.g. to achieve low random access delays during memory operation.

In an embodiment, the tape further comprises a bulk material, preferably polyethylene naphthalate, PEN.

In an embodiment, one or more surface regions of the tape are configured to store the data.

For example, the surface region of the tape comprises a functional layer that can be read out / written to by the data head.

In an embodiment, the data head is arranged over a top side of the tape opposite to the bottom side.

In particular, the data head is arranged over the surface regions that store the data.

In an embodiment, in a first mode of the storage device, the data head is configured to read and/or write data from and/or to the tape while the tape is stationary; and, in a second mode of the storage device, the data head is configured to read and/or write data from and/or to the tape while the tape is moving.

In an embodiment, the storage device further comprises two cavities which are arranged, in the length direction, in front and behind the actuator, respectively; wherein each cavity is configured to receive a part of the tape, in particular an end part of the tape.

In an embodiment, the storage device is configured to fold the tape in each cavity. This achieves the advantage that the overall size of the storage device can be reduced. In particular, a tape with a length of up to <NUM> can be folded to a much smaller size. In particular, the cavity only needs to be big enough to accommodate the folded tape.

In an embodiment, the storage device further comprises a number of folding electrodes arranged in each cavity, wherein the folding electrodes are configured to fold the tape. This achieves the advantage that the tape can be folded and unfolded in an efficient manner for a compact storage of the tape.

According to a second aspect, the present disclosure relates to a storage system comprising a plurality of storage devices according to the first aspect of the present disclosure embedded in a substrate.

Embodiments of the invention will be explained in the followings together with the figures.

<FIG> shows a schematic diagram of a storage device <NUM> according to an embodiment.

The storage device <NUM> comprises a tape <NUM> configured to store data, a data head <NUM> configured to read and/or write data from and/or to the tape <NUM>, and an actuator <NUM> configured to move the tape <NUM> in a length direction in a step-wise manner. The actuator <NUM> comprises a number of pulling electrodes <NUM>, wherein each pulling electrode <NUM> can be activated to exert a pulling force on the tape <NUM>, and a number of clamping electrodes <NUM>, wherein each clamping electrode <NUM> can be activated to clamp the tape <NUM>.

The actuator <NUM> may be a linear stepper motor that translates mechanical deformation of the tape <NUM>, i.e. bending, into a net forward or backward displacement.

The pulling electrodes <NUM> and the clamping electrodes <NUM> may be configured, if activated, to excerpt an attractive electrostatic force on the tape <NUM>. The actuator <NUM> can be configured to move the tape in the step-wise manner by activating and deactivating the number of pulling electrodes <NUM> and clamping electrodes <NUM> according to a defined activation sequence.

Each of the pulling electrodes <NUM> respectively clamping electrodes <NUM> is activated by applying a defined pulling voltage respectively clamping voltage to the electrodes <NUM>, <NUM>.

The storage device <NUM> that is depicted in <FIG> comprises three clamping electrodes <NUM> and two pulling electrodes <NUM>, which are alternately arranged along the length of the tape <NUM>. However, a different number of pulling and clamping electrodes <NUM>, <NUM> is also possible. In general, the actuator <NUM> comprises at least one pulling electrode <NUM> and two clamping electrodes <NUM> to be able to move the tape.

The tape <NUM> may be a flexible micro- or nanosheet for storing data, for example, a parallel flexible nanosheet storage. The tape <NUM> can also be a tube or a rod with a certain flexibility that allows deformation. The length of the tape <NUM> may be varied from millimeters to centimeters.

The tape <NUM> can be made of a polymer film or foil, for example polyethylene naphthalate or polyimide.

The tape <NUM> can comprise a functional layer for data storage on its top side for example, the functional layer may comprise a storage element that can be read out / written to by the data head.

The tape <NUM> may be configured to store data based on various different storage strategies, for example immobilized charges (similar to flash), topographic storage (e.g., generated by thermomechanical indentation of the tape surface), phase-change storage, magnetic storage, ferro-electric storage, resistive storage or electromechanical storage. The data head <NUM> can be configured to read/write data from/to the tape <NUM> according to the storage strategy. The data head <NUM> can be a read/write array.

The data head <NUM> can be arranged over the top side of the tape <NUM> in a data module <NUM> of the storage device <NUM>. The data module <NUM> can be comprised in or connected to the actuator <NUM>.

The tape <NUM>, preferably, comprises a conductive layer <NUM> on its bottom side. This conductive layer <NUM> may be configured as a counter electrode for the electrostatic actuation by the pulling electrodes <NUM> and clamping electrodes <NUM>, which are arranged below the bottom side of the tape <NUM>. The conductive layer <NUM> can be a continuous metallic thin film or an intrinsically conductive polymer (ICP) film.

A stepped or latched operation of the actuator <NUM> is performed by sequentially applying AC or DC voltages (in the range of <NUM> to <NUM> volt) between the clamping respectively pulling electrodes <NUM>, <NUM> and the counter-electrode <NUM> of the tape <NUM>.

<FIG> shows schematic diagrams of the storage device <NUM> according to further embodiments.

Thereby, <FIG> shows an out-of-plane, i.e. vertically arranged, version of the storage device <NUM> and <FIG> shows an in-plane, i.e. horizontally arranged, version of the storage device <NUM>.

The out-of-plane arrangement of the storage device <NUM>, as shown in <FIG>, has the advantage that a surface area that is occupied by the actuator <NUM> can be decreased with respect to the planar arrangement. Thus, a larger number of storage devices <NUM> could be integrated in a certain area. Thereby, each out-of-plane storage device could have a tape <NUM> with a shorter length, leading to an overall higher area enhancement and/or lower access times.

In the storage devices <NUM> of this disclosure, e.g. as shown in <FIG>, the pulling electrodes <NUM> are arranged at a further distance from the tape <NUM> than the clamping electrodes <NUM>. In particular, in the storage device <NUM> shown in <FIG>, the pulling electrodes <NUM> are recessed with respect to the clamping electrodes <NUM> to support the movement of the tape.

If activated, each pulling electrode <NUM> is configured to deform a section of the tape <NUM> by pulling said section away from a longitudinal axis of the tape <NUM>. This deformation results in a pulling force on the tape <NUM> towards the activated pulling electrode <NUM>. By clamping the tape <NUM> on one side of the activated pulling electrode <NUM>, the tape <NUM> is only pulled from the other (not-clamped) side resulting in a lateral movement of the non-clamped side of the tape <NUM> towards the pulling electrode <NUM>.

Furthermore, the tape <NUM> may exhibit an internal stiffness that, additionally, supports the tape <NUM> movement after this deformation. In particular, after the pulling electrode <NUM> is deactivated again, the deformed tape reverses the deformation due to its internal stiffness, causing a pushing force on the tape. By clamping the tape <NUM> on the other side of the deactivated pulling electrode <NUM>, the internal stiffness pushes the tape <NUM> further in the length direction. The internal stiffness of the tape <NUM> may mostly stem from its bulk material <NUM>, which can be polyethylene naphthalate (PEN).

Further, the internal stiffness of the tape <NUM> can be modulated by at least one additional counter-electrode (not shown in <FIG>) on the opposite side of the tape, i.e. above the top side of the tape <NUM>.

The length of the pulling and clamping electrodes <NUM>, <NUM> can be in the range of <NUM> to <NUM>. In particular, the pulling electrode <NUM> is longer than the clamping electrode <NUM>.

The storage device <NUM> as shown in <FIG> may further comprise two cavities <NUM> which are arranged, in the length direction, in front and behind the actuator <NUM>, respectively. Each of these cavities <NUM> may receive an end part of the tape <NUM>. In particular, the end parts of the tape <NUM> can be folded in each cavity, which allows reducing the form factor of the storage device <NUM>.

The storage device <NUM> may comprise a number of folding electrodes <NUM> that are arranged in each cavity <NUM>. The folding electrodes <NUM> can be configured to guide a controlled stacking or folding of the tape <NUM> in the cavities <NUM>.

Furthermore, the actuator <NUM> may comprise additional stator electrodes for an increased motor control, such as capacitive displacement sensing for closed loop operation.

The storage device <NUM> as shown in any one of the previous <FIG>, <FIG> can form an electrostatic shuffle driven mechanical memory device. Such a storage device <NUM> combines several advantages, in particular, when compared to other commonly used memory or actuation concepts:.

Further, the actuator <NUM>, in principle, can allow for an unlimited displacement range with nanometer resolution. In addition, the storage device <NUM> can be inherently shock resistant, because the tape <NUM> may be clamped to the actuator <NUM> at any point in time. This may also prevent undesired resonances and vibration rejection.

Lastly, the actuator <NUM> can be scalable. In particular, electrostatic step motors, generally, have favorable scaling characteristics (max. operational frequency increases to MHz when scaling to the micro domain). Electrostatic pull and push forces in order of mN can still be reachable on the microscale. This is, particularly, an advantage over electromagnetic motors that do not scale well into the micro-domain, because they require permanent magnets and have a high energy consumption to operate.

<FIG> shows a schematic diagram of a possible activation sequence of the actuator <NUM> of the storage device <NUM> according to an embodiment.

In particular, <FIG> shows an actuation sequence for the pulling electrodes <NUM> and clamping electrodes <NUM> for moving the tape <NUM> for one step. The actuator <NUM> of the storage device <NUM> in <FIG> comprises one center clamping electrode <NUM>-<NUM>, two outer clamping electrodes <NUM>-<NUM>, <NUM>-<NUM>, and two pulling electrodes <NUM>-<NUM>, <NUM>-<NUM>, which are arranged in-between the clamping electrodes <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>. The activation sequence shown in <FIG> can be executed by any one of the storage devices <NUM> shown in <FIG>, <FIG>.

In a first step (step <NUM>), the tape is clamped by the central clamping electrode <NUM>-<NUM>, which is arranged directly below the data head <NUM>.

In a second step (step <NUM>), pulling electrode <NUM>-<NUM> is additionally activated. This causes a section of the tape <NUM> to be pulled into the recession of the pulling electrode <NUM>-<NUM> and, thus, results in a pulling of the (not-clamped) side of the tape <NUM> towards the pulling electrode. Thereby, the tape is laterally pulled by a length of Δlateral towards the pulling electrode <NUM>-<NUM>.

In a third step (step <NUM>), the central clamping electrode <NUM>-<NUM> is deactivated and the two outer clamping electrodes <NUM>-<NUM> and <NUM>-<NUM> are activated.

In a fourth step (step <NUM>), the pulling electrode <NUM>-<NUM> is deactivated and the pulling electrode <NUM>-<NUM> is activated instead, causing the tape <NUM> to move under the data head towards pulling electrode <NUM>-<NUM>.

In a fifth and final step (step <NUM>), the central clamping electrode <NUM>-<NUM> is reactivated and all other electrodes are deactivated, causing the tape <NUM> to stiffen-up and be pushed away from the central clamping electrode <NUM>-<NUM> by its internal stiffness.

The steps <NUM> to <NUM> result in one movement step of the tape <NUM> by a lateral distance of Δlateral. By cyclically repeating steps <NUM>-<NUM>, the tape can be moved under the data head <NUM> in a quick and precise manner. For example, tape step frequencies between <NUM> and several MHz as well as nanometer positioning accuracies over the complete displacement range of the storage medium (mm to cm) can be achieved.

By regulating the pulling voltage that is applied to the pulling electrodes <NUM>-<NUM>, <NUM>-<NUM>, an operating mode of the actuator <NUM> can be set to a fine stepping mode or to a fast stepping mode, respectively.

<FIG> shows schematic diagrams of a part of the actuator <NUM> of the storage device <NUM> operating in two different modes according to an embodiment. In particular, <FIG> shows the actuator <NUM> in the fine stepping mode and <FIG> shows the actuator <NUM> in the fast stepping mode.

<FIG> show a part of the actuator with one pulling electrode <NUM> and two clamping electrodes <NUM>. The pulling electrode <NUM> is arranged in a recess <NUM> of height hclamp with respect to the clamping electrodes <NUM> and has a length of L. Further, a dielectric layer <NUM> of thickness tdiel is arranged over the pulling electrode <NUM>. In both <FIG>, the left clamping electrode <NUM> is activated (clamped) and the right clamping electrode <NUM> is deactivated (roller).

In the fine stepping mode (<FIG>), the pulling voltage may be smaller than a threshold value. The threshold value can correspond to the pulling voltage Vpull-in that is required so that the tape <NUM> is in contact with the dielectric layer <NUM>, i.e. the tape <NUM> is pulled to the bottom of the recess <NUM> and touches said bottom.

In particular, when the pulling electrode <NUM> is activated, two forces are acting on the tape <NUM>. The first force is the electrostatic force that causes the deformation of the tape <NUM>. In particular, the first force is a "surface force" or "pressure force", i.e. normalized to the surface of the pulling electrodes <NUM>, and can be described by: <MAT>.

Here, εo is the vacuum permittivity, V is the voltage applied to the pulling electrode <NUM>, w is the deflection of the tape <NUM> towards the pulling electrode <NUM>, and geff is a factor that is calculated by: <MAT> with εdiel being the relative permittivity of the dielectric layer <NUM>. The second force is a restoring force due to the internal stiffness of the tape <NUM> that can be described by: <MAT>.

Here, Etape is the Young's modulus of the tape <NUM> and Itape is the area moment of inertia of the tape <NUM>.

If the pulling electrode <NUM> is activated the tape <NUM> is pulled down until a force balance (qmech + qel = o) is reached. Solving the force balance equation for the deflection w, allows to calculate the distance by which the tape is moved in a length direction in each movement step by: Δlateral = <NUM> - w<NUM>/L.

In the fine stepping mode shown in <FIG>, the step size of the tape <NUM> can be minimized, by reducing the voltage applied to the pulling electrode <NUM> and, thus, the deflection w of the tape <NUM>. In this way, a nanometer resolution position control with respect to the data head <NUM> may be achieved over the complete displacement range of the storage medium, which can be in the range from millimeters to centimeters.

In the fast stepping mode (<FIG>), the pulling voltage may exceed the threshold value. Therefore, a section of the deformed tape of length Lcontact is in contact with the bottom of the recess <NUM>, wherein Lcontact = L - Leff. Thus, the mechanical stiffness (spring constant) of the tape <NUM> is defined by the two non-contact regions <NUM>, each having a length of Leff/<NUM>.

This changes the electrostatic force that causes the deformation of the tape <NUM> to: <MAT> and the restoring force to: <MAT>.

Solving the force balance equation for the non-contact region Leff, allows to calculate the distance by which the tape is moved in length direction in each step according to: Δlateral = <NUM> · hclamp<NUM>/Leff.

In particular, in the fast stepping mode the tape speed can be enhanced by enhancing the voltage applied to the pulling electrode <NUM> and, thus, decreasing the size of the non-contact region Leff, causing an enhancement of the lateral displacement Δlateral. Thereby, high velocities (~ m/s) for low random access delays during memory operation (~ milliseconds) can be achieved.

<FIG> shows schematic diagrams of a storage system <NUM> according to an embodiment. Thereby, <FIG> is a top view and <FIG> is a perspective view of the storage system <NUM>.

The storage system <NUM> comprises a plurality of storage devices <NUM> embedded in a substrate <NUM>. The plurality of storage devices <NUM> can, thereby, be arranged according to a square lattice with an x-pitch and a y-pitch.

Such a storage system <NUM> can form a data memory, e.g. for a handheld device.

The storage devices <NUM> can be arranged vertically, according to an out-of-plane arrangement, to increase the density of the storage devices <NUM>. For example, each storage device <NUM> can be embedded in a cavity of the substrate <NUM> in a vertical manner.

Each of the storage devices <NUM> of the system <NUM> may comprise an actuator <NUM> which can move (push/pull operation) the flexible tape <NUM> (nanotape or nanotube) over a data head <NUM>. For a fixed in-plane density, the required tape <NUM> length can be dependent on the density of the storage devices <NUM>. The typical in-plane dimension of the storage device <NUM> is of the order of microns, while the length of the tape <NUM> can be varied from millimeters to centimeters. In this way, tape <NUM> densities of <NUM><NUM> to <NUM><NUM>/mm<NUM> can be achieved.

<FIG> shows a line chart highlighting the relationship between the tape <NUM> dimensions and the arrangement of the storage devices <NUM> in the storage system <NUM> according to an embodiment.

In particular, <FIG> shows the relationship between the tape <NUM> length and the x-pitch of the storage devices <NUM> in a storage system <NUM> as shown in <FIG>. For example, <FIG> relates to a storage system <NUM> with an in-plane storage density of <NUM> Tb/mm<NUM>. Thereby, a bit pitch of <NUM> and a y-pitch driver efficiency (see <FIG>) of <NUM> is assumed. Folding strategies can allow for longer tapes or tubes to be enclosed in low-profile memory packages (< <NUM> thickness).

When scaling down the size of each storage device <NUM>, more devices <NUM> can be present in the same overall area. If the total storage capacity is fixed, for example to <NUM> Tb/mm<NUM>, the length of the tape <NUM> can be decreased for each storage device <NUM>. Eventually when scaling to a critical dimension, the tape <NUM> lengths for a certain storage density becomes shorter than half the height of the storage system <NUM>. As this point, no tape folding is required (indicated by the dashed line in <FIG>), thus, simplifying the implementation. Here, scaling may refer to equal scaling of absolute X-pitch and Y-pitch as indicated in <FIG>, e.g. assuming the maximum width of the tape is <NUM>% of the full Y-pitch (~ Y-efficiency = <NUM>%).

<FIG> shows a schematic diagram of the storage system <NUM> according to another embodiment.

In particular, <FIG> shows a cross-sectional view of a storage system <NUM>, where the storage devices are embedded in a substrate <NUM>, which comprises a silicon wafer <NUM>, a MEMS layer <NUM>, and top and bottom encapsulation layers <NUM>, <NUM>.

Claim 1:
A storage device (<NUM>), comprising:
a tape (<NUM>) configured to store data;
a data head (<NUM>) configured to read and/or write data from and/or to the tape (<NUM>); and
an actuator (<NUM>) configured to move the tape (<NUM>) in a length direction in a step-wise manner, wherein the actuator (<NUM>) comprises:
a number of pulling electrodes (<NUM>), wherein each pulling electrode (<NUM>) is configured to be activated to exert a pulling force on the tape (<NUM>), and
a number of clamping electrodes (<NUM>), wherein each clamping electrode (<NUM>) is configured to be activated to clamp the tape (<NUM>);
wherein
the pulling electrodes (<NUM>) and the clamping electrodes (<NUM>) are alternately arranged along the length of the tape (<NUM>),
the pulling electrodes (<NUM>) are arranged at a further distance from the tape (<NUM>) than the clamping electrodes (<NUM>), and
if activated, each pulling electrode (<NUM>) is configured to deform a section of the tape (<NUM>) by pulling said section away from a longitudinal axis of the tape (<NUM>), wherein said deformation causes the pulling force on the tape (<NUM>).