BACKGROUND

Recently, the “Internet of Things” (IoT) has been one of the most popular research topics in both academia and industry. IoT addresses the network of physical objects which can be controlled and interacted with wirelessly through the support of current computer technologies, such as: Bluetooth, Wi-Fi, smart phones, and cloud computing. IoT technologies aim to improve user experiences and efficiency, and seek to reduce power consumption across a variety of applications, such as medical monitoring and food supply. In IoT technologies, the sub-field of wearable systems has attracted increasing research interest due to its many applications and wearable systems' ability to provide a profound impact on people's daily lives. Wearable systems have been emerging for broad applications and have significant market potential. However, one of the major technical challenges for wearable technology is power management. Moreover, a physical connection, such as wired charging and wired communication should be minimized in wearable technology. As a result, wearable devices with long battery life and life span are preferred.

Traditionally, wearable electronics systems are powered by lithium-ion batteries or other external power sources. However, these power sources are less than ideal because lithium-ion batteries have a significant environmental impact and external power sources rely on wiring that degrades the user experience with wearable devices. These issues have stimulated efforts to develop self-powered portable wearable electronics that can be utilized in building a sustainable wearable system. Many of these efforts focus on developing high efficiency wearable power generators. The power management systems for these wearable technologies play a key role in the self-powered system. Thus, high voltage devices, i.e., transistors, are fundamental components in the power control circuits for the power management components of self-powered wearable systems.

SUMMARY

Wearable electronics have broad applications, such as personal health and wellness and have a profound impact on people's daily lives. Wearable electronics rely on power and three major energy sources have been investigated for possible nano-generators (power generators) for wearable electronics: (i) biomechanical energy from the movement of the wearable device user, (ii) solar energy, and (iii) thermal energy from the temperature difference between the wearable device user, e.g., human, and surrounding environment. However, the conventional power controller that these nano-generators rely on is bulky and undesirable for use with wearable electronics. The existing power controllers are also built on rigid substrates, separated from the nano-generators and also require additional wiring to connect to the nano-generators. For wearable systems, it is desired to integrate nano-generators with the power control device on a single flexible substrate, such as a plastic or fabric/textile substrates. Such an integrated self-powered wearable system is small in size, flexible, eliminates the need for external wiring between nano-generators and the power controller, and enables recharging of flexible batteries and the direct driving of electronics under vastly different environmental conditions.

To develop a flexible power management component for wearable electronics, a high voltage transistor fabricated on a flexible substrate at a low process temperature is needed. Embodiments of the present invention provide such a flexible high voltage thin film transistor (f-HVTFT) that can be utilized in the power management component of self-powered wearable systems. Embodiments can be integrated with wearable power generators to charge wearable batteries or directly drive other wearable electronic devices, such as sensors, actuators, and communication platforms.

One such embodiment of the present invention is directed to a f-HVTFT having a bottom gate configuration. In such an embodiment, the f-HVTFT comprises a flexible substrate with a ring-shaped gate on the flexible substrate and an insulating gate dielectric layer on the gate and the flexible substrate. Such an embodiment of the f-HVTFT also includes a ring-shaped semiconductor channel on the insulating gate dielectric layer and a ring-shaped source and a circular drain, wherein the source, the drain, and the gate are concentric and the source and the drain are over the insulating gate dielectric layer with the ring-shaped semiconductor channel between said source and drain, and where, there is an offset region between the circular drain and the ring-shaped gate. Such an embodiment also includes a source electrode pad with multiple connections to the ring-shaped source and a gate electrode pad with multiple connections to the ring-shaped gate. Another embodiment of the f-HVTFT has two offset regions, one between the drain and gate and another between the gate and source.

According to an embodiment, the flexible substrate of the f-HVTFT is transparent and thus, the f-HVTFT is also transparent. In another embodiment, the flexible substrate is opaque and thus, in such an embodiment, the flexible and bendable f-HVTFT is not totally transparent. In an example embodiment, the flexible substrate is composed of at least one of: polyimide, plastics, polyethylene naphthalate (PEN), textiles, paper, metal and bendable glass.

In yet another embodiment of the f-HVTFT, a given electrode pad, i.e., the source electrode pad and/or gate electrode pad, has multiple connections, equally distributed in perpendicular directions, to its respective transistor component terminals, e.g. the source or the gate.

Embodiments of the f-HVTFT and elements thereof may be composed of a variety of materials. In an embodiment, the channel of the f-HVTFT is composed of at least one oxide semiconductor. According to such an embodiment, the oxide semiconductor channel may be composed of at least one of: Zinc Oxide (ZnO), pure ZnO, doped ZnO, ZnO based semiconductor heterostructures, and ZnO alloys. In yet another embodiment, the oxide semiconductor channel is composed of Magnesium Zinc Oxide (MgxZn1-xO) where 0<x<0.06. This channel composition, according to an embodiment, enhances the thermal stability, negative bias stress (NBS) stability, and threshold voltage stability of the f-HVTFT's operation.

In yet another embodiment, the insulating gate dielectric layer is composed of at least one of: Silicon Dioxide (SiO2), Aluminum Oxide (Al2O3), Hafnium Oxide (HfO2), and Magnesium Oxide (MgO). In an alternative embodiment, the insulating gate dielectric layer is a multi-layer dielectric stacking structure composed of at least one of: SiO2, Al2O3, HfO2, and MgO. In an embodiment, the effective thickness of the multi-layer dielectric stacking structure is configured to allow the f-HVTFT to satisfy requirements of both (i) high blocking voltage and (ii) sufficient on-current. For example, in an embodiment the multi-layer dielectric stacking structure has an effective thickness between 50 nm and 300 nm. In yet another embodiment, the insulating gate dielectric layer of the f-HVTFT has a thickness between 50 nm and 300 nm.

Embodiments of the f-HVTFT are fabricated at temperatures that are compatible with the materials that comprise the device. For instance, in an embodiment, the process for fabricating the f-HVTFT is performed at temperatures compatible with the flexible substrate comprising at least one of: polyimide, plastics, PEN, textiles, paper, and bendable glass. This manufacturing technique ensures the integrity of the f-HVTFT.

In an embodiment, the ring shaped gate, ring shaped source, and circular drain of the f-HVTFT are center-symmetric. This symmetry is advantageous because it prevents electric field crowding and also enhances the strength of the f-HVTFT against bending along random directions.

As described herein, embodiments can be incorporated into the power management components of self-powered wearable electronic systems. In one such implementation, the f-HVTFT provides the sufficient on-current (˜10 μA) and the high blocking voltage (˜100V) to match the output characteristics of the energy sources, e.g., triboelectric nano-generators and wearable solar cells, amongst others, of wearable devices. According to an embodiment, the f-HVTFT has a small leakage current which enables low standby power consumption that is important to self-powered wearable systems.

Embodiments of the f-HVTFT described herein having a bottom gate configuration can be employed in a variety of applications. For instance, an embodiment of the f-HVTFT can be used in an inverter of a microelectromechanical system (MEMS). Likewise, in another embodiment, the f-HVTFT is used in an inverter to drive an actuator. Further still, embodiments of the f-HVTFT may be used in a flexible power management system employed in a mobile phone and/or a flexible display. Yet another embodiment of the f-HVTFT is used in a three-dimensional vertically integrated circuit. In such an embodiment, employing the f-HVTFT in the vertically integrated circuit reduces the overall size of the circuit. Another embodiment of the present invention is directed to a self-powered wearable system that includes a power management component that includes a f-HVTFT as described herein. Similarly, yet another embodiment is directed to a portable and wearable system that includes a f-HVTFT to provide blocking voltage and on-current matching output characteristics of a nano-generator coupled to the wearable system.

Another embodiment of the present invention is directed to a flexible diode (f-diode) that is achieved by connecting the gate and drain of the f-HVTFTs described, through the metallization process during the fabrication. Such reconfiguration and reconnection can be done in embodiments of the bottom gate f-HVTFT and top gate f-HVTFT described herein. In one such embodiment, the f-diode includes a flexible substrate, a ring-shaped gate on the flexible substrate, and an insulating gate dielectric layer on the gate and the flexible substrate. Such a flexible diode also includes a ring-shaped oxide semiconductor channel on the insulating gate dielectric layer, a circular source, and a ring-shaped drain, wherein the source, the drain, and the gate are concentric and the source and the drain are over the insulating gate dielectric layer with the ring-shaped oxide semiconductor channel between said source and drain, and where, there is an offset region between the circular source and the ring-shaped gate and a terminal of the ring-shaped drain is connected to a terminal of the ring-shaped gate. Such a flexible diode embodiment also includes a drain electrode pad with multiple connections to the ring-shaped drain and a gate electrode pad with multiple connections to the ring-shaped gate.

An embodiment of the invention is directed to a transformerless DC/DC converter implemented as a power management component of a self-powered wearable system. The DC/DC converter includes a f-HVTFT with a bottom gate configuration and a flexible diode. The f-HVTFT in the DC/DC converter includes a flexible substrate, a ring-shaped gate on the flexible substrate, an insulating gate dielectric layer on the gate and the flexible substrate, a ring-shaped oxide semiconductor channel on the insulating gate dielectric layer, a ring-shaped source, and a circular drain, wherein the source, the drain, and the gate are concentric and the source and the drain are over the insulating gate dielectric layer with the ring-shaped oxide semiconductor channel between said source and drain, and where, there is an offset region between the circular drain and the ring-shaped gate. Moreover, the f-HVTFT includes a source electrode pad having multiple connections to the ring-shaped source and a gate electrode pad having multiple connections to the ring-shaped gate. The flexible diode in the DC/DC converter comprises a given flexible substrate, a given ring-shaped gate on the given flexible substrate, a given insulating gate dielectric layer on the given gate and the given flexible substrate, a given ring-shaped oxide semiconductor channel on the given insulating gate dielectric layer, a given circular source and a given ring-shaped drain, wherein the given source, the given drain, and the given gate are concentric and the given source and the given drain are over the given insulating gate dielectric layer with the given ring-shaped oxide semiconductor channel between said given source and given drain, and where, there is a given offset region between the given circular source and the given ring-shaped gate and a terminal of the given ring-shaped drain is connected to a terminal of the given ring-shaped gate. Further, the flexible diode in the DC/DC converter comprises a given drain electrode pad having multiple connections to the given ring-shaped drain and a given gate electrode pad having multiple connections to the given ring-shaped gate. According to an embodiment of the DC/DC converter, the flexible diode of the DC/DC converter separates input and output of the DC/DC converter.

Yet another embodiment of the present invention is directed to a DC/AC inverter implemented as a power management component of a self-powered wearable system. Such a DC/AC inverter embodiment includes a plurality of f-HVTFTs and a plurality of flexible diodes. Each f-HVTFT includes a flexible substrate, a ring-shaped gate on the flexible substrate, an insulating gate dielectric layer on the gate and the flexible substrate, a ring-shaped oxide semiconductor channel on the insulating gate dielectric layer, a ring-shaped source, and a circular drain, wherein the source, the drain, and the gate are concentric and the source and the drain are over the insulating gate dielectric layer with the ring-shaped oxide semiconductor channel between said source and drain, and where, there is an offset region between the circular drain and the ring-shaped gate. Further, each f-HVTFT includes a source electrode pad having multiple connections to the ring-shaped source and a gate electrode pad having multiple connections to the ring-shaped gate. Each flexible diode of the plurality of flexible diodes includes a given flexible substrate, a given ring-shaped gate on the given flexible substrate, a given insulating gate dielectric layer on the given gate and the given flexible substrate, a given ring-shaped oxide semiconductor channel on the given insulating gate dielectric layer, a given circular source, and a given ring-shaped drain, wherein the given source, the given drain, and the given gate are concentric and the given source and the given drain are over the given insulating gate dielectric layer with the given ring-shaped oxide semiconductor channel between said given source and given drain, and where, there is a given offset region between the given circular source and the given ring-shaped gate and a terminal of the given ring-shaped drain is connected to a terminal of the given ring-shaped gate. Each flexible diode also includes a given drain electrode pad having multiple connections to the given ring-shaped drain and a given gate electrode pad having multiple connections to the given ring-shaped gate. In such a DC/AC inverter embodiment, the inverter is formed through connecting respective pairings each comprising a given flexible diode of the plurality of flexible diodes and a given f-HVTFT of the plurality of f-HVTFTs. According to an embodiment, in each respective pairing, the given flexible diode and the given f-HVTFT are connected in parallel.

Another embodiment of the present invention is directed to a center-symmetric f-HVTFT having a top gate configuration. In embodiments, the top gate f-HVTFT may have the same operating principle as embodiments of the bottom-gated f-HVTFT. Moreover, embodiments of the top gate f-HVTFT may be achieved by changing the order of the layers of the bottom-gated f-HVTFT counterpart and the corresponding process steps. Furthermore, embodiments of the top gate f-HVTFT may be employed in the same applications as embodiments of the bottom gate f-HVTFT described herein.

According to an embodiment, a f-HVTFT having a top gate configuration includes a flexible substrate, an insulating layer on the flexible substrate, and a ring-shaped semiconductor channel on the insulating layer. The f-HVTFT with a top gate configuration also includes a ring-shaped source and a circular drain, wherein the source and the drain are concentric and the source and the drain are over the insulating layer and in contact with the ring-shaped semiconductor channel, an insulating gate dielectric layer on the ring-shaped oxide semiconductor channel, a ring-shaped gate on the insulating gate dielectric layer, wherein there is an offset region between the ring-shaped gate and the circular drain and where, the gate, the source, and the drain are concentric, and also includes a source electrode pad with multiple connections to the ring-shaped source and a gate electrode pad having with connections to the ring-shaped gate.

According to an embodiment, the flexible substrate of the f-HVTFT having a top gate configuration is transparent and thus, the f-HVTFT is also transparent. In another embodiment, the flexible substrate is opaque. In an embodiment of the f-HVTFT having a top gate configuration, the flexible substrate is composed of at least one of: polyimide, plastics, PEN, textiles, paper, and bendable glass.

In yet another embodiment, a given electrode pad, i.e., the source electrode pad and/or gate electrode pad, has multiple connections, equally distributed in perpendicular directions, to its respective component, e.g. the source or the gate.

Embodiments of the f-HVTFT with the top gate configuration and elements thereof may be composed of a variety of materials. In an embodiment, the channel is composed of at least one oxide semiconductor. According to such an embodiment, the oxide semiconductor channel may be composed of at least one of: ZnO, pure ZnO, doped ZnO, ZnO based semiconductor heterostructures, and ZnO alloys. In yet another embodiment, the oxide semiconductor channel is composed of MgxZn1-xO where 0<x<0.06.

In yet another embodiment, the insulating gate dielectric layer is composed of at least one of: SiO2, Al2O3, HfO2, and MgO. In an alternative embodiment, the insulating gate dielectric layer is a multi-layer dielectric stacking structure composed of at least one of: SiO2, Al2O3, HfO2, and MgO. In an embodiment of the f-HVTFT having a top gate configuration, the multi-layer dielectric stacking structure has an effective thickness between 50 nm and 300 nm. In yet another embodiment, the insulating gate dielectric layer has a thickness between 50 nm and 300 nm.

Embodiments of the f-HVTFT with a top gate configuration are fabricated at temperatures that are compatible with the materials that comprise the device. For instance, in an embodiment, the f-HVTFT is fabricated at temperatures compatible with the flexible substrate comprising at least one of: polyimide, plastics, PEN, textiles, paper, metal and bendable glass.

Embodiments of the f-HVTFT described herein having a top gate configuration can be employed in a variety of applications. For instance, an embodiment of the f-HVTFT can be used in an inverter of a MEMS device. Likewise, in another embodiment, the f-HVTFT is used in an inverter of an actuator. Further still, embodiments of the top gate f-HVTFT may be used in a flexible power management system employed in a mobile phone and/or a flexible display. Yet another embodiment of the f-HVTFT having a top-gate configuration is used in a three-dimensional vertically integrated circuit. An embodiment of the present invention is directed to a self-powered wearable system that includes a power management component that includes a f-HVTFT with a top gate configuration as described herein. Similarly, yet another embodiment is directed to a portable and wearable system that includes a f-HVTFT with a top gate configuration to provide blocking voltage and on-current matching output characteristics of a nano-generator coupled to the wearable system.

An alternative embodiment of the present invention is directed to a flexible diode that comprises a flexible substrate, an insulating layer on the flexible substrate, a ring-shaped oxide semiconductor channel on the insulating layer, a ring-shaped source and a circular drain, wherein the source and the drain are concentric and the source and the drain are over the insulating layer and in contact with the ring-shaped oxide semiconductor channel, an insulating gate dielectric layer on the ring-shaped oxide semiconductor channel, a ring-shaped gate on the insulating gate dielectric layer, wherein there is an offset region between the ring-shaped gate and the ring-shaped source and where, the gate, the source, and the drain are concentric and a terminal of the gate is connected to a terminal of the drain, and a source electrode pad with multiple connections to the ring-shaped source and a gate electrode pad with multiple connections to the ring-shaped gate.

Another embodiment of the present invention is directed to a transformer-less DC/DC converter implemented in a power management component of a self-powered wearable system. An embodiment of the DC/DC converter includes a f-HVTFT with a top gate configuration and a flexible diode. In such an embodiment of the DC/DC converter, the f-HVTFT comprises a flexible substrate, an insulating layer on the flexible substrate, a ring-shaped oxide semiconductor channel on the insulating layer, a ring-shaped source and a circular drain, wherein the source and the drain are concentric and the source and the drain are over the insulating layer and in contact with the ring-shaped oxide semiconductor channel. The f-HVTFT in such an embodiment also includes an insulating gate dielectric layer on the ring-shaped oxide semiconductor channel, a ring-shaped gate on the insulating gate dielectric layer, where there is an offset region between the ring-shaped gate and the circular drain and where, the gate, the source, and the drain are concentric, and a source electrode pad with multiple connections to the ring-shaped source and a gate electrode pad with multiple connections to the ring-shaped gate. Further, the flexible diode of the DC/DC converter comprises a given flexible substrate, a given insulating layer on the given flexible substrate, a given ring-shaped oxide semiconductor channel on the given insulating layer, a given ring-shaped source and a given circular drain, wherein the given source and the given drain are concentric and the given source and the given drain are over the given insulating layer and in contact with the given ring-shaped oxide semiconductor channel, a given insulating gate dielectric layer on the given ring-shaped oxide semiconductor channel, a given ring-shaped gate on the given insulating gate dielectric layer, where there is a given offset region between the given ring-shaped gate and the given ring-shaped source and where, the given gate, the given source, and the given drain are concentric and a terminal of the given gate is connected to a terminal of the given drain. The flexible diode in such an embodiment also includes a given source electrode pad with multiple connections to the given ring-shaped source and a given gate electrode pad with multiple connections to the given ring-shaped gate. According to an embodiment of the DC/DC converter, the flexible diode separates input and output of the DC/DC converter.

Yet another embodiment is directed to a DC/AC inverter implemented in a power management component of a self-powered wearable system. The DC/AC inverter includes a plurality of f-HVTFTs with a top gate configuration and a plurality of flexible diodes where the inverter is formed through connecting respective pairings each comprising a given flexible diode of the plurality of flexible diodes and a given f-HVTFT of the plurality of f-HVTFTs. In such an embodiment, each f-HVTFT of the plurality comprises a flexible substrate, an insulating layer on the flexible substrate, a ring-shaped oxide semiconductor channel on the insulating layer, a ring-shaped source and a circular drain, where the source and the drain are concentric and the source and the drain are over the insulating layer and in contact with the ring-shaped oxide semiconductor channel. Each f-HVTFT also includes an insulating gate dielectric layer on the ring-shaped oxide semiconductor channel, a ring-shaped gate on the insulating gate dielectric layer, wherein there is an offset region between the ring-shaped gate and the circular drain and where, the gate, the source, and the drain are concentric, and, further, a source electrode pad with multiple connections to the ring-shaped source and a gate electrode pad with multiple connections to the ring-shaped gate. Moreover, in a DC/AC inverter embodiment, each flexible diode of the plurality comprises a given flexible substrate, a given insulating layer on the given substrate, a given ring-shaped oxide semiconductor channel on the given insulating layer, a given ring-shaped source and a given circular drain, wherein the given source and the given drain are concentric and the given source and the given drain are over the given insulating layer and in contact with the given ring-shaped oxide semiconductor channel, a given insulating gate dielectric layer on the given ring-shaped oxide semiconductor channel, a given ring-shaped gate on the given insulating gate dielectric layer, wherein there is a given offset region between the given ring-shaped gate and the given ring-shaped source and where, the given gate, the given source, and the given drain are concentric and a terminal of the given gate is connected to a terminal of the given drain. Each flexible diode also includes a given source electrode pad with multiple connections to the given ring-shaped source and a given gate electrode pad having with connections to the given ring-shaped gate. According to an embodiment, in each respective pairing, the given flexible diode and the given f-HVTFT are connected in parallel.

It is noted that herein, the aspects of the f-HVTFT, such as materials and dimensions, may be modified so as to perform optimally for each specific application.

