Patent Publication Number: US-9842643-B2

Title: Apparatuses, methods, and systems for dense circuitry using tunnel field effect transistors

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a divisional of U.S. patent application Ser. No. 14/575,962, filed Dec. 18, 2014, entitled “APPARATUSES, METHODS, AND SYSTEMS FOR DENSE CIRCUITRY USING TUNNEL FIELD EFFECT TRANSISTORS,” the entire disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     Embodiments of the present invention relate generally to the technical field of electronic circuits, and more particularly to circuitry using devices having asymmetric conduction properties, e.g., tunnel field effect transistors (TFETs). 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in the present disclosure and are not admitted to be prior art by inclusion in this section. 
     In a multiple power supply design, it may often be necessary for logic circuits to signal across voltage domains. A low-overhead solution may be particularly important where separate technologies operate at different supply voltages. For example, in an integrated circuit chip, memory cells including low voltage components may operate at a different supply voltage than other portions of the chip including higher voltage components. Current voltage level shifting circuits may be effective, but have drawbacks including significant delay, area, and power overhead. In addition, current voltage level shifting circuits also may require both low and high voltage supplies to operate. Routing power supply wires between regions dedicated to separate voltage domains is challenging and inefficient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements. Embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings. 
         FIG. 1  is a circuit diagram of a voltage level shifter including one or more switching devices having asymmetric conductive properties in accordance with various embodiments. 
         FIG. 2  is circuit diagram of another voltage level shifter including one or more switching devices having asymmetric conductive properties in accordance with various embodiments. 
         FIG. 3  is a circuit diagram of a memory cell including one or more switching devices having asymmetric conductive properties in accordance with various embodiments. 
         FIG. 4  is a circuit diagram of another memory cell including one or more switching devices having asymmetric conductive properties in accordance with various embodiments. 
         FIG. 5  is an example layout of a portion of a memory array including a memory cell similar to the memory cell of  FIG. 3  in accordance with various embodiments. 
         FIG. 6  is an example layout of a portion of a memory array including a memory cell similar to the memory cell of  FIG. 4  in accordance with various embodiments. 
         FIG. 7  illustrates an example system configured to employ the apparatuses and methods described herein, in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof wherein like numerals designate like parts throughout, and in which is shown by way of illustration embodiments that may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of embodiments is defined by the appended claims and their equivalents. 
     Various operations may be described as multiple discrete actions or operations in turn, in a manner that is most helpful in understanding the claimed subject matter. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations may not be performed in the order of presentation. Operations described may be performed in a different order than the described embodiment. Various additional operations may be performed and/or described operations may be omitted in additional embodiments. 
     For the purposes of the present disclosure, the phrases “A and/or B” and “A or B” mean (A), (B), or (A and B). For the purposes of the present disclosure, the phrase “A, B, and/or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C). 
     The description may use the phrases “in an embodiment,” or “in embodiments,” which may each refer to one or more of the same or different embodiments. Furthermore, the terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments of the present disclosure, are synonymous. 
     As used herein, the term “circuitry” may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and/or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable hardware components that provide the described functionality. As used herein, “computer-implemented method” may refer to any method executed by one or more processors, a computer system having one or more processors, a mobile device such as a smartphone (which may include one or more processors), a tablet, a laptop computer, a set-top box, a gaming console, and so forth. 
     As used herein, the term “inverter” may broadly encompass pairs of transistors with drain terminals coupled to an output terminal and gate terminals coupled to an input terminal. In embodiments, associated source terminals may not need to be directly attached to supply voltage (Vdd) or ground (GND) supply levels. 
       FIG. 1  is a circuit diagram of a voltage level shifter  100  in accordance with various embodiments. In embodiments, voltage level shifter  100  may include a charging circuit portion  110  (or, which may be thought of as a ‘sending portion’) having an input node  125  that may receive an input signal INP (also referred to as low voltage signal INP) associated with a low voltage domain and a receiver circuit portion  117  having an output terminal  150  to produce an output signal OUT which may be a high voltage signal and associated with a high voltage domain. The input signal INP may be, for example, a data signal, a control signal, or another signal that is to be transmitted from the low voltage domain to the high voltage domain. Note that although example voltages may be given, the terms “low voltage” and “high voltage” may be used here as relative terms to each other without limiting the terms to actual values. In various embodiments, charging circuit portion  110  may include a driving circuit which in the embodiment shown may be a first inverter  105  while receiver circuit portion  117  may include a second inverter  115 . In various embodiments, the driving circuit may include inverter  105  and/or other logic gates including, but not limited to a NOT AND (“NAND”) or NOT OR (“NOR”) gate. In embodiments, the first inverter  105  may be coupled to the input node  125  to receive the input signal INP. The first inverter  105  may include complementary first and second transistors p 0  and n 0 , each having asymmetric conduction properties. For example, in embodiments, first inverter  105  may include a P-type tunnel field-effect transistor (P-TFET) coupled in series with second inverter n 0  which may be an N-type tunnel field-effect transistor (N-TFET). In the embodiment, first inverter  105  may be coupled between a low voltage supply (350 millivolts (“mV”)) and ground. 
     In embodiments, second inverter  115  may also include complementary transistors coupled in series, a third transistor p 1  and a fourth transistor n 1 . In embodiments, the third transistor p 1  and a fourth transistor n 1  may include respectively first and second metal-oxide-semiconductor field-effect transistor (MOSFET) devices such for example, a P-type metal-oxide-semiconductor field-effect transistor (PMOS) transistor and an N-type metal-oxide-semiconductor field-effect (NMOS) transistor. As shown in the embodiment, second inverter  115  may be coupled between a higher voltage supply or “high voltage supply” (e.g., 600 mV) and ground. In embodiments, a feedback transistor p 2 , which in the embodiment shown may be a PMOS transistor, may be coupled to an output terminal of second inverter  115 . Feedback transistor p 2  may also have a source terminal coupled to the high voltage supply, and a drain terminal coupled to the output terminal of first inverter  105  in embodiments. 
     In embodiments, when low voltage signal INP may be received at input node  125 , first transistor p 0  may be activated or switched “on.” In the embodiment, output signal OUT may charge to 350 mV, causing the output of the second inverter  115  of receiver circuit portion  117  to transition to a lower voltage. For the embodiments, feedback transistor p 2  may be activated which may then pull output signal OUT up to 600 mV. In embodiments, when output signal OUT may be at 600 mV, first transistor p 0  may have a source to drain voltage Vsd of −250 mV. Accordingly, at this bias voltage, first transistor p 0 , which may in embodiments have asymmetric conduction properties as a P-TFET, may not conduct from source to drain. In embodiments, a short circuit path between the lower voltage supply and the higher voltage supply may be prevented. Note that in embodiments, a magnitude of a voltage difference between the low and high voltage domains may be limited by thresholds of first and second inverters  105  and  115  and a writability of output signal OUT. Although the operation of voltage level shifter  100  is discussed herein using specific example values for the low voltage supply and the high voltage supply, it will be apparent that the voltage level shifter  100  may be used with any suitable values for the low voltage supply and the high voltage supply. Note that in embodiments, second inverter  115  and feedback transistor p 2  may be considered a feedback circuit. 
       FIG. 2  is circuit diagram of a voltage level shifter  200  in accordance with various embodiments. As shown in the embodiment, charging circuit portion  210  including an inverter  205  may be similar to charging circuit portion  110  of  FIG. 1  and may include complementary first and second transistors p 0  and n 0  having asymmetric conduction properties. In embodiments, receiver circuit portion  217 , however, may include additional circuitry compared with the receiver circuit portion  117  of  FIG. 1 , to provide integrated isolation functionality. In addition to a complementary third and fourth transistors n 1  and p 1 , in embodiments, voltage level shifter  200  may further include a logic firewall including an enable input terminal  220  coupled to an input terminal of transistors p 3  and n 3 , also referred to as devices  218 . In embodiments, devices  218  may be coupled with second inverter  215  to form a NOT AND (NAND) gate. In embodiments, a feedback transistor p 2  may be coupled to the output terminal of first inverter  205  and an output terminal of the NAND gate. 
     Accordingly, in embodiments, a voltage level shifter such as for example, voltage lever shifter  100  or  200  may interface between a lower or low voltage logic domain, such as for example a TFET domain, communicating with a higher voltage logic domain, such as for example, a CMOS domain. Accordingly, the present embodiments illustrate an example where the voltage level shifter may be unidirectional and one or more switching devices or transistors may conduct asymmetrically to prevent crossover of a high voltage signal into a low voltage domain. Note that in embodiments, the voltage level shifter may be able to operate entirely with the high voltage domain, avoiding challenges associated with routing the lower voltage domain into the higher voltage domain. 
     Note that in various embodiments, a strength of a feedback transistor such as for example, feedback transistor p 2 , may be decreased by using a higher threshold transistor or adding additional feedback transistors similar to feedback transistor p 2  in series to allow for cell-writability. Further, note that although various transistors have been shown as a P-type or N-type of switching device, this may be only for illustrative purposes. For example, in the present example the low voltage domain and the high voltage domain may share a common ground between them. In other embodiments, a common supply voltage may be used at different ground levels. Thus, transistors in various roles that may be shown here as e.g. a P-type device, may, in other embodiments, be an N-type device, and vice-versa. 
       FIG. 3  is a circuit diagram of a memory cell  300  including one or more switching devices having asymmetric conductive properties such as for example, one or more TFETs, in accordance with various embodiments. In embodiments, memory cell  300  may be a static random access memory (SRAM) cell included in a memory array of a plurality of SRAM cells. In embodiments, memory cell  300  may be a seven-transistor ( 7 -T) voltage cell including a first write transistor WN 1  and a second write transistor WN 2  coupled at a respective first and second drain to a respective first inverter  301  and second inverter  303 . First inverter  301  and second inverter  303  may form a cross-coupled pair of inverters. In embodiments, first write transistor WN 1  and second write transistor WN 2  may be coupled at their sources to a write word line  312  which may carry a write word line signal WWL. In embodiments, a read access transistor RAC may be coupled at its source to a read word line  314  which may carry a signal RWL and at a gate  305  to an output of the second inverter  303 . In embodiments, first inverter  301  may include a pull-up transistor PU 1  coupled in series to a pull-down transistor PD 1 , while second inverter  303  may include a pull-up transistor PU 2  coupled in series to a pull-down transistor PD 2 . 
     In embodiments, a bit line  316  which may carry a bit line signal BL and an inverse bit line  318  which may carry an inverse bit line signal XBL may be coupled to run vertically on a respective first and second side of memory cell  300 . For the embodiment, bit line  316  may be coupled to a gate of the first write transistor WN 1  and the inverse bit line  318  may be coupled to a gate of the second write transistor WN 2  to receive a signal associated with a write operation. Note that in contrast, in an SRAM  6 -T memory cell, a bit line may be coupled to a source of a write transistor, rather than a gate. For the embodiment, a voltage assist line  310  which may carry a signal ASSIST_VDD may be coupled to first inverter  301  and second inverter  303  to assist the write operation. In the embodiment, voltage assist line  310  may be coupled to independently address a memory word. In embodiments, voltage assist line  310  may carry a signal ASSIST_GND (not shown) and be coupled to pull-down transistors or devices of the cross-coupled pair of inverters. In embodiments, first write transistor WN 1 , second write transistor WN 2 , pull-up transistor PU 1 , pull-down transistor PD 1 , pull-up transistor PU 2 , pull-down transistor PD 2 , and read access transistor RAC may be TFETs. In embodiments, pull-up transistors PU 1  and PU 2  may be P-type TFETS (P-TFETs) while pull-down transistors PD 1  and PD 2  may be N-type TFETs (N-TFETs). 
     In embodiments, during the write operation, selection of memory cell  300  may be indicated by a transition in a write word line signal WWL to a low voltage level. In the embodiment, bit line signal BL may be at a voltage supply level Vdd, while inverse bit line signal XBL may be at ground. Accordingly, for the embodiment, first write transistor WN 1  may switch “on” or be activated, while second write transistor WN 2  may not. In embodiments, first write transistor WN 1  may begin to switch output of inverter  301 . Thus, in embodiments, it may be desirable to weaken pull-up transistor PU 1  relative to first write transistor WN 1 . Thus, in embodiments, voltage assist line  310  may be reduced in magnitude or deactivated (e.g., brought to a value of 0 Volts). Note that in embodiments, a layout of memory cell  300  allows voltage assist line  310  to be turned off for a single word. Note that in various embodiments, first write transistor WN 1  or second write transistor WN 2  may be turned on based on a state of bit line signal BL and inverse bit line signal XBL respectively. In embodiments, because voltage assist line  310  may be deactivated, bit line  316  or inverse bit line  318  may be able to fully discharge a storage node. Next, voltage assist line  310  may be activated (e.g., brought to a value of Vdd). In embodiments, once voltage assist line  310  may be activated, depending on a state of bit line  316  and inverse bit line  318 , pull-up transistor PU 1  or pull-up transistor PU 2  may assist in writing the memory cell  300 . 
     Accordingly, in embodiments, voltage assist line  310  may be deactivated to assist a write operation for individual words. In embodiments, this may allow memory cell  300  to be written despite possible variation and mismatch between transistors. In other embodiments, voltage assist line  310  may be coupled to a ground terminal of at least one of cross-coupled inverters, first inverter  301  and second inverter  303 , and be deactivated to assist a write operation. In embodiments, deactivation may refer to a full or partial switching of a voltage level (e.g. a reduction in magnitude). Thus, in embodiments, where voltage assist line  310  may be coupled to a ground potential, deactivation may refer to the voltage level being raised partially or fully toward Vdd. 
       FIG. 4  is a circuit diagram of another memory cell  400  in accordance with various embodiments. In embodiments memory cell  400  may operate with similar principles to memory cell  300  of  FIG. 3 , however, memory cell  400  may use both a P-type device and an N-type device to perform a write operation, enabling a robust writing of logic 1 and a logic 0 at low voltages. In embodiments, the write operation may be written to one inverter of a cross-coupled pair of inverters including first inverter  401  and second or “feedback” inverter  403 . As shown, first inverter  401  may include a pull-up transistor PU 1  and a pull-down transistor PD 1  while feedback inverter  403  may include a pull-up transistor PU 2  and a pull-down transistor PD 2 . In embodiments, a write word line  410  associated with a write word line signal WWL and an inverse write word line  412  associated with an inverse write word line signal WWL# may run along a first side (in the example shown, horizontally) along memory cell  400 . In the embodiment, write word line  410  and inverse write word line  412  may act as voltage supplies for feedback inverter  403 . In other embodiments, write word line  410  and inverse write word line  412  may also provide first inverter  401  with ground and Vdd supplies, respectively. In addition, a write bit line  416  and a read bit line  418  associated with respective write bit line signal WBL and read bit line signal RBL may run vertically in the present embodiment, along opposing sides of memory cell  400 . In embodiments, write bit line  416  may be coupled to a “write inverter”  405  which may include a complementary pair of write transistors, first write transistor WN and second write transistor WP. As shown, write bit line  416  may be coupled to a gate of first write transistor WN and a gate of second write transistor WP. In embodiments, first write transistor WN may be an N-type TFET while second write transistor WP may be a P-type TFET. 
     In embodiments, during a write operation, write word line signal WWL may be asserted by transitioning to a high voltage level and inverse write word line signal WWL# may be asserted by transitioning to a low voltage level. In the embodiment, feedback inverter  403  may be deactivated and write inverter  405  may be activated. In embodiments, first write transistor WN or second write transistor WP may write to a storage node Q. In embodiments, first write transistor WN and second write transistor WP may be able to substantially fully switch the storage node Q because a positive voltage supply of write word line  410  may be turned on or activated. In embodiments, inverse write word line signal WWL# and word line signal WWL may be de-asserted and transition to a respective high voltage level and low voltage level. In embodiments, feedback inverter  403  may be activated and write inverter  405  may be deactivated. During a transition of write word line signal WWL and inverse write word line signal WWL#, a state of memory cell  400  may be momentarily held static by substantially only pull-up transistor PU 1  and pull-down transistor PD 1  of first inverter  401 . In various embodiments, in order to ensure robustness, a second set of a write word line and an inverse write word line may be independently controlled in an overlapping fashion as voltage supplies for feedback inverter  403  (not shown in figure). 
     Note that in embodiments, memory cells  300  and  400  may have separate read and write transistors to eliminate a read instability. Furthermore, in embodiments, memory cell  300  and  400  may have a layout that allows significantly more density than comparable memory cells. For example,  FIG. 5  illustrates an example layout  500  of a portion of a memory array including a plurality of bit cells or memory cells similar to memory cell  300  of  FIG. 3 . In an embodiment, as shown in a lower right corner of  FIG. 5 , memory cell layout  501  illustrates a memory cell layout of a single memory cell  300 . In the embodiment, example layout  500  includes bit cells  501 ( a ),  501 ( b ),  501 ( c ), and  501 ( d ) which have a memory cell layout  501 . For the embodiment, Legend  530  illustrates differently shaded areas corresponding to device source and drain structure for memory cell layout  501 . In embodiments, source and drain terminals in  501 ( a )- 501 ( d ) which are adjacent may be configured to carry common electrical signals so that spacing between bit cells can be minimized in the memory array associated with layout  500 . In embodiments, layout  500  may enable dense memory cells where a memory cell or bit cell, such as for example, bit cell  501 ( a ) of a word may abut a next bit cell  501 ( b ) of the same word along a long edge  512  of bit cell  501 ( a ) and bit cell  501 ( b ). In embodiments, a bit cell  501 ( c ) in a same bit position may abut another bit cell  501 ( a ) in the same bit position along a short edge  515  of bit cell  501 ( c ) and bit cell  501 ( a ). In embodiments, a plurality of lines indicated at arrows  517  may run parallel to short edges of the plurality of bit cells  501 ( a )- 501 ( d ) and may include word lines and ground. In embodiments, a plurality of lines indicated at arrows  519  may run parallel to long edges of the plurality of bit cells  501 ( a )- 501 ( d ) and may include bit lines and inverse bit lines. In embodiments, the transistor gates in memory cell layout  501  may run parallel to the long edge of a bit cell. 
     Next,  FIG. 6  illustrates an example layout  600  of a portion of a memory array including a plurality of bit cells or memory cells similar to memory cell  400  of  FIG. 4 . In an embodiment, as shown on a right side of  FIG. 6 , a memory cell layout  601  illustrates a memory cell layout of a single memory cell  400 . In the embodiment, layout  600  includes bit cells  601 ( a ),  601 ( b ),  601 ( c ), and  601 ( d ) which have a memory cell layout  601 . For the embodiment, Legend  630  may illustrate differently shaded areas corresponding to device source and drain structure for memory cell layout  601 . In embodiments, source and drain terminals in  601 ( a )- 601 ( d ) which are adjacent may be configured to carry common electrical signals so that spacing between bit cells can be minimized in an array associated with layout  600 . In embodiments, layout  600  may enable dense memory cells where a bit cell  601 ( a ) may have a layout that is flipped along a long edge  612  so that bit cell  601 ( b ) may have a mirror image of the layout of bit cell  601 ( a ). Similarly, in embodiments, bit cells  601 ( c ) and  601 ( d ) may have layouts that are mirror images of each other along long edge  612 . In embodiments, a plurality of lines indicated at arrows  617  may run parallel to short edges of the plurality of bit cells  601 ( a )- 601 ( d ) and may include word lines and ground. In embodiments, a plurality of lines indicated at arrows  619  may run parallel to long edges of the plurality of bit cells  601 ( a )- 601 ( d ) and may include bit lines and inverse bit lines. In embodiments, transistor gates of layout  601  may run parallel to long edges of a bit cell corresponding to memory cell layout  601 . 
       FIG. 7  illustrates an example computing device  700  that may employ the apparatuses and/or methods described in connection with the above in accordance with various embodiments. As shown, computing device  700  may include a memory array  760  and a voltage level shifter  770 . In embodiments, memory array  760  may include one or more memory cells such as, for example, memory cell  300  or memory cell  400  as described in connection with  FIG. 3  and  FIG. 4 . In embodiments, voltage level shifter  770  may include a voltage level shifter, such as for example, voltage level shifter  100  or voltage level shifter  200  as described in connection with  FIG. 1  and  FIG. 2 . 
     Computing device  700  may further include a number of components such as one or more processor(s)  704  (one shown). In embodiments, memory array  760  may be located in a cache of processor  704 . In embodiments, voltage level shifter  770  may be coupled to memory array  760  which may be located in a low voltage domain to allow memory array  760  to communicate with a high voltage domain in or associated with one or more processor(s)  704 . In various embodiments, memory array  760  and/or voltage level shifter  770  may be located in other suitable blocks in computing device  700  where similar memory arrays may be used and/or communication between a low voltage domain and a high voltage domain may occur. For example, memory array  760  may be included in graphics processor  516  or any of memory controller  505 , I/O controller  514 , or touchscreen controller  522 . In embodiments, foltage level shifter  770  may be included in the processor  704  and/or another component of computing device  700  to convert signals between a low voltage domain and a high voltage domain. 
     In various embodiments, the one or more processor(s)  704  each may include one or more processor cores. In various embodiments, at least one communication chip  706  may be physically and electrically coupled to the one or more processor(s)  704 . In further implementations, the communication chip  706  may be part of the one or more processor(s)  704 . In various embodiments, computing device  700  may include printed circuit board (PCB)  702 . For these embodiments, the one or more processor(s)  704  and communication chip  706  may be disposed thereon. In alternate embodiments, the various components may be coupled without the employment of PCB  702 . Depending on its applications, computing device  700  may include other components that may or may not be physically and electrically coupled to the PCB  702 . These other components include, but are not limited to, memory controller  705 , volatile memory (e.g., dynamic random access memory (DRAM)  708 ), non-volatile memory such as read only memory (ROM)  710 , flash memory  712 , storage device  711  (e.g., a hard-disk drive (HDD)), an I/O controller  714 , a digital signal processor (not shown), a crypto processor (not shown), a graphics processor  716 , one or more antenna  718 , a display (not shown), a touch screen display  720 , a touch screen controller  722 , a battery also referred to as power supply  724 , an audio codec (not shown), a video codec (not shown), a global positioning system (GPS) device  728 , a compass  730 , an accelerometer (not shown), a gyroscope (not shown), a speaker  732 , a camera  734 , and a mass storage device (such as hard disk drive, a solid state drive, compact disk (CD), digital versatile disk (DVD)) (not shown), and so forth. In various embodiments, the processor  704  may be integrated on the same die with other components to form a System on Chip (SoC). 
     In some embodiments, the one or more processor(s)  704 , flash memory  712 , and/or storage device  711  may include associated firmware (not shown) storing programming instructions configured to enable computing device  700 , in response to execution of the programming instructions by one or more processor(s)  704 , to practice all or selected aspects of the methods described herein. The communication chips  706  may enable wired and/or wireless communications for the transfer of data to and from the computing device  700 . The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. The communication chip  706  may implement any of a number of wireless standards or protocols, including but not limited to IEEE 702.20, Long Term Evolution (LTE), LTE Advanced (LTE-A), General Packet Radio Service (GPRS), Evolution Data Optimized (Ev-DO), Evolved High Speed Packet Access (HSPA+), Evolved High Speed Downlink Packet Access (HSDPA+), Evolved High Speed Uplink Packet Access (HSUPA+), Global System for Mobile Communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Digital Enhanced Cordless Telecommunications (DECT), Worldwide Interoperability for Microwave Access (WiMAX), Bluetooth, derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. The computing device  700  may include a plurality of communication chips  706 . For instance, a first communication chip  706  may be dedicated to shorter range wireless communications such as Wi-Fi and Bluetooth, and a second communication chip  706  may be dedicated to longer range wireless communications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others. 
     In various implementations, the computing device  700  may be a laptop, a netbook, a notebook, an ultrabook, a smartphone, a computing tablet, a personal digital assistant (PDA), an ultra-mobile PC, a mobile phone, a desktop computer, a server, a printer, a scanner, a monitor, a set-top box, an entertainment control unit (e.g., a gaming console or automotive entertainment unit), a digital camera, an appliance, a portable music player, or a digital video recorder. In further implementations, the computing device  700  may be any other electronic device that processes data. 
     Some non-limiting Examples are provided below. 
     Example 1 is a circuit to shift a voltage level, comprising: a driving circuit associated with a low voltage domain and including a transistor, wherein the transistor is coupled to, in response to an input signal, pass a signal associated with the low voltage domain to an output terminal of the driving circuit; and a feedback circuit associated with a high voltage domain, wherein a terminal of the feedback circuit is coupled to the output terminal of the driving circuit to receive the signal associated with the low voltage domain and produce a voltage level on a terminal referenced to the high voltage domain, wherein the transistor of the driving circuit to conduct asymmetrically to prevent crossover of a high voltage signal into the low voltage domain. 
     Example 2 is the circuit of Example 1, wherein the feedback circuit includes a feedback transistor with a first terminal coupled directly or indirectly to a high voltage supply, a second terminal coupled to the output terminal of the driving circuit, and a third terminal coupled to a logic gate associated with the high voltage domain. 
     Example 3 is the circuit of Example 2, wherein the feedback transistor is a first feedback transistor of a pair of feedback transistors coupled in series to the high voltage supply. 
     Example 4 is the circuit of Example 2, wherein the feedback circuit includes an inverter coupled at an output terminal to the feedback transistor. 
     Example 5 is the circuit of Example 1, wherein the transistor of the driving circuit includes a P-type tunnel field effect transistor (P-TFET) and/or an N-type tunnel field effect transistor (N-TFET). 
     Example 6 is the circuit of Example 1, wherein the feedback circuit includes metal-oxide-semiconductor field-effect transistor (MO SFET) devices. 
     Example 7 is the circuit of Example 1, wherein the driving circuit is an inverter coupled between a low voltage supply and ground and wherein the inverter includes a P-type tunnel field effect transistor (P-TFET) coupled in series with an N-type tunnel field effect transistor (N-TFET). 
     Example 8 is the circuit of Example 1, further including a logic firewall coupled to the feedback circuit to allow a voltage supply of the low voltage domain to turn off. 
     Example 9 is the circuit of Example 8 wherein the feedback transistor is coupled between the output terminal of the driving circuit and an output terminal of a NOT AND (NAND) gate. 
     Example 10 is a circuit to shift a voltage level, comprising: a transistor having a gate terminal coupled to receive a control signal and a source terminal and a drain terminal coupled to enable a first voltage signal to pass in response to the control signal; an inverter having an input terminal coupled to the drain terminal of the transistor to receive the first voltage signal from the transistor, wherein the transistor enables voltage signals including the first voltage signal to pass substantially only in a first direction; and a feedback transistor having a gate terminal coupled to receive the first voltage signal from an output terminal of the inverter and to produce a second voltage signal. 
     Example 11 is the circuit of Example 10, wherein the first voltage signal includes a low voltage domain signal and the second voltage signal includes a high voltage domain signal. 
     Example 12 is the circuit of Example 10, wherein the transistor comprises a first transistor, and wherein the first transistor comprises a P-type tunnel field-effect transistor (P-TFET) and is coupled in series with a second transistor, wherein the second transistor comprises an N-type tunnel field-effect transistor (N-TFET). 
     Example 13 is the circuit of Example 10, wherein the inverter is coupled between a high voltage supply and ground and includes a first metal oxide semiconductor field-effect transistor (MOSFET) transistor coupled to a second MOSFET transistor. 
     Example 14 is a memory array, comprising: a plurality of static random access memory (SRAM) cells each including a cross-coupled pair of inverters including a first inverter having complementary first and second transistors and a second inverter having complementary third and fourth transistors; a first write transistor and a second write transistor coupled to the respective first and second inverter to write a value to a storage node of the first inverter or the second inverter; and a voltage assist line coupled to one or more of the first and second cross-coupled pair of inverters to change a voltage level to assist the first write transistor or the second write transistor write the value to the storage node, wherein the voltage assist line is coupled to independently address a memory word. 
     Example 15 is the memory array of Example 14, wherein the complementary first and second transistors, the complementary third and fourth transistors, and the write transistors are tunnel field effect transistors (TFETs). 
     Example 16 is the memory array of Example 14, further comprising a bit line and an inverse bit line coupled to the plurality of SRAM cells, wherein the bit line is coupled to a gate of the first write transistor and the inverse bit line is coupled to a gate of the second write transistor to receive a signal associated with a write operation. 
     Example 17 is the memory array of Example 14, further comprising a read access transistor coupled at a source to a read word line and at a gate to an output of the second inverter. 
     Example 18 is the memory array of Example 14, wherein the complementary first and second transistors and complementary third and fourth transistors have a source-drain doping configuration to enable a first memory cell of a word to abut a second memory cell of the word along a long edge of the first memory cell and the second memory cell. 
     Example 19 is the memory array of Example 14, further comprising one or more word lines oriented in a direction perpendicular to a direction of a gate orientation of the first write transistor and the second write transistor and further comprising one or more bit lines oriented in a direction parallel to the direction of the gate orientation of the first write transistor and the second write transistor. 
     Example 20 is a memory array, comprising: a plurality of static random access memory (SRAM) cells each including a cross-coupled inverter pair including a first inverter and a second inverter; and a third inverter coupled to the second inverter of the cross-coupled inverter pair, the third inverter including a complementary first and second write transistor, each coupled at a first and second respective gates to a same bit line to write a value to one side of the cross-coupled inverter pair. 
     Example 21 is the memory array of Example 20, further comprising a first word line and a second word line, wherein the first word line and the second word line are coupled to provide a voltage supply to at least the second inverter and the third inverter. 
     Example 22 is the memory array of Example 21, wherein the first word line and the second word line are activated or deactivated to assist the complementary first and second write transistor to perform a write operation. 
     Example 23 is the memory array of Example 22, wherein the first word line and the second word line are coupled to independently address a memory word. 
     Example 24 is the memory array of Example 20, wherein the complementary first and second write transistors include a P-type tunnel field effect transistor (P-TFET) and an N-type tunnel field effect transistor (N-TFET). 
     Example 25 is the memory array of Example 20, further comprising one or more word lines coupled to the memory array, wherein the one or more word lines are oriented in a direction perpendicular to a gate orientation of the first and second respective gates and wherein the bit line is oriented in a direction parallel to the gate orientation of the first and second respective gates. 
     Example 26 is a system, comprising: a first circuit component including a high voltage domain; a second circuit component including a low voltage domain; and a driving circuit associated with the low voltage domain and including a transistor, wherein the transistor is coupled to, in response to an input signal, pass a signal associated with the low voltage domain to an output terminal of the driving circuit; and a feedback circuit associated with the high voltage domain, wherein a terminal of the feedback circuit is coupled to the output terminal of the driving circuit to receive the signal associated with the low voltage domain and produce a high voltage signal, wherein the transistor of the driving circuit conducts asymmetrically to prevent crossover of the high voltage signal into the low voltage domain. 
     Example 27 is the system of Example 26, wherein the second circuit component including the low voltage domain includes a memory array. 
     Example 28 is the system of Example 27, wherein the memory array comprises: a plurality of static random access memory (SRAM) cells each including a cross-coupled inverter pair including a first inverter and a second inverter; and a third inverter coupled to the second inverter of the cross-coupled inverter pair, the third inverter including a complementary first and second write transistor, each coupled at a first and second respective gates to a same bit line to write a value to a storage node. 
     Although certain embodiments have been illustrated and described herein for purposes of description, this application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that embodiments described herein be limited only by the claims. 
     Where the disclosure recites “a” or “a first” element or the equivalent thereof, such disclosure includes one or more such elements, neither requiring nor excluding two or more such elements. Further, ordinal indicators (e.g., first, second, or third) for identified elements are used to distinguish between the elements, and do not indicate or imply a required or limited number of such elements, nor do they indicate a particular position or order of such elements unless otherwise specifically stated.