Patent Publication Number: US-2023155550-A1

Title: Piezo-resistive resonator device having drive and sense transistors with wells of opposite doping

Description:
BACKGROUND 
     To generate high frequency (e.g., 1-10 GHz) clock signals required in processors (e.g., CPUs, GPUs), cascaded phase lock loop circuits (PLLs) may be used to multiply an external reference clock with a frequency of 25 MHz to 100 MHz. The cascaded PLLs may be a source of a long term jitter (e.g., jitter with a periodicity over tens of cycles of the GHz clock), which can degrade the processor&#39;s performance. In addition, due to extra low jitter requirements of certain devices (e.g., wireless RF transceivers or high frequency wireline transceivers), these circuits may also require integrated PLLs that use inductors in their oscillator. However, the integrated inductors do not usually have very high Q factors, take up large silicon areas, cause crosstalk, and have no possibilities for scaling. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A- 1 B  illustrate aspects of an example piezo-resistive resonator (PZR) device in accordance with embodiments of the present disclosure. 
         FIGS.  2 A- 2 D  illustrate example operational aspects of a PZR in accordance with embodiments of the present disclosure. 
         FIGS.  3 A- 3 B  illustrate example transistor configurations for a PZR device in accordance with embodiments of the present disclosure. 
         FIGS.  4 A- 4 B  illustrate example circuit modeling for the transistor configurations of  FIGS.  3 A- 3 B , respectively. 
         FIGS.  5 A- 5 C  illustrate example PZR devices with different drive:sense ratios in accordance with embodiments of the present disclosure. 
         FIGS.  6 A- 6 B  illustrate example simulation data for the transistor configurations shown in  FIGS.  3 A- 3 B . 
         FIG.  7    illustrates an example PZR device with a varactor as a drive circuit in accordance with embodiments of the present disclosure. 
         FIG.  8    is a block diagram of an example electrical device that may include a microelectronic assembly, in accordance with any of the embodiments disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     As described above, certain processor devices may include cascaded PLLs to multiply an external reference clock with a frequency of 25 MHz to 100 MHz to obtain a clock signal on the order of ˜1-10 GHz. In some instances, the PLLs may include inductors in their oscillator; however, these inductors do not usually have very high Q factors, take up large silicon areas, cause crosstalk, and have no possibilities for scaling. In embodiments described herein, FET-based resonators (e.g., piezo-resistive resonators (PZRs)) may be used as a low-jitter frequency source for PLL circuits. 
     A PZR device according to the present disclosure may include a resonant circuit in which drive transistor(s) are mechanically coupled to sense transistor(s) by a shared gate. An RF frequency signal on the drive transistor causes an oscillating mechanical stress across the drive transistor&#39;s gate dielectric due to capacitive actuation. At certain drive frequencies, there is a mechanical resonance where the frequency is determined by the gate pitch (which may refer to the distance between two adjacent gates/fins, e.g., in a multiple transistor device as described herein) and material properties of the gate material. The mechanical resonance propagates down the length of the shared gate where it causes a piezo-resistive effect on the channel of the sense transistor. The resonance can then be detected at the sense transistor where the oscillating stress modulates the channel mobility and therefore the channel current. 
     To avoid the potential of the drive signal “feeding through” the substrate and appearing at the sense transistor, embodiments herein may implement the drive and sense transistors in wells of opposite doping, reducing the feed-through of the drive signal into the sense transistor(s) (via the pn junction that is formed between the two oppositely-doped wells). Conduction may accordingly be reduced, e.g., due to the higher resistance of the junction compared to the resistance of the substrate. In addition, in certain embodiments, the drive transistor may operate in the accumulation mode, which can accommodate higher operating frequencies for the resonator device. 
       FIGS.  1 A- 1 B  illustrate aspects of an example piezo-resistive resonator (PZR) device in accordance with embodiments of the present disclosure. In particular,  FIG.  1 A  illustrates a tri-gate transistor with a source or drain node  109  coupled to a channel of a fin, which then couples to a corresponding drain or source node. Source and drain nodes are connected to contacts  110 ,  111 . Spacers  106 ,  108  are located between the gate  105  and the source/drain nodes, which are on top of substrate  107 . More particularly, the transistor of  FIG.  1 A  is a fin-based field-effect transistor (FinFET) formed around a thin strip of semiconductor material (referred to as the “fin”). The fin is formed on layer  107 . Layer  107  may be a substrate, oxide, and the like. In some embodiments, the fin may be formed from the substrate. The FinFET includes MOSFET nodes: gate  105 , gate dielectric  113  (see  FIG.  1 B ), and source and drain regions. The source and drain regions may be highly doped (with epitaxial growth in some embodiments). A conductive channel of the FinFET resides on the outer sides of the fin beneath the gate dielectric. Current runs along both “sidewalls” of the fin as well as along the top side of the fin. Because the conductive channel essentially resides along the three different outer, planar regions of the fin, the particular FinFET of  FIG.  1 A  is typically referred to as a “tri-gate” FinFET. Other types of FinFETs exist (such as “double-gate” FinFETs, which may be included in other embodiments and in which the conductive channel principally resides only along both sidewalls of the fin and not along the top side of the fin). 
       FIG.  1 B  includes a series of tri-gate FinFETs similar to the FinFET of  FIG.  1 A  that collectively form a resonator device. Specifically,  FIG.  1 B  shows a cross-sectional view of a multi-fin structure on the x-y plane with z at the fin center.  FIG.  1 B  includes a tri-gate transistor with a drain node  109  coupled to a channel  119  of a fin, which then couples to a corresponding source node  112 . Channel  119  couples to gate dielectric  113  and gate  105 . Other transistors include drain nodes  116 ,  117 , channels  120 ,  121  (all of which couple to gate  105  via separate gate dielectric portions), and source nodes  114 ,  115 . Although  FIG.  1 B  includes three transistors, other embodiments may include additional or fewer transistors, e.g., as described below. 
       FIGS.  2 A- 2 D  illustrate example operational aspects of a PZR in accordance with embodiments of the present disclosure. In particular,  FIG.  2 A  depicts a parallel plate capacitor model for modeling resonator actuation in embodiments of the present disclosure. The driving schemes for a PZR (modeled by the capacitor of  FIG.  2 A ) include: 
     
       
         
           
             
               F 
               
                 a 
                 ⁢ 
                 c 
               
             
             = 
             
               
                 
                   ϵ 
                   ⁢ 
                   A 
                 
                 
                   d 
                   2 
                 
               
               ⁢ 
               
                 V 
                 
                   D 
                   ⁢ 
                   C 
                 
               
               ⁢ 
               
                 v 
                 
                   i 
                   ⁢ 
                   n 
                 
               
             
           
         
       
     
     where d, ϵ, A, V DC , and v in  respectively correspond to gap thickness, permittivity, capacitor area, DC bias, and AC bias, and result in actuation  141  due to actuation force F ac . 
       FIG.  2 B  depicts capacitive actuation  151 ,  152  in embodiments of the present disclosure. A voltage V DD  may be supplied to gate  105  and an AC voltage may be input at source  112 /drain  109  to induce capacitive actuation  151 ,  152  across the gate dielectric  113 . The high-k dielectric  113  helps provide a larger F ac  for the same bias inputs. The V DD  DC input is used to create capacitance across the fin and the dielectric  113 . 
       FIG.  2 C  depicts mechanical resonance within the gate  105  of a multi tri-gate resonator in embodiments of the present disclosure. As a result of the actuation shown in  FIG.  2 B , mechanical resonance occurs within the gate  105 . In the example shown, line  132  corresponds to longitudinal displacement of the gate  105  and line  131  corresponds to dynamic stress within the gate  105 . 
       FIG.  2 D  depicts piezoresistive sensing in a PZR in embodiments of the present disclosure. To sense the periodic stress  131 , the gate  105  is biased with V DD  (which may help provide capacitance and generate an inversion layer for the channels that couple sources/drains to one another) and a DC bias (V bias ) is applied to the drain  109  to flow current  141  through the fin. When the gate  105  resonates, the DC current  141  is piezoresistively modulated by the dynamic tensile/compressive stress  131  within the fin. 
       FIGS.  3 A- 3 B  illustrate example transistor configurations for a PZR device in accordance with embodiments of the present disclosure. In particular,  FIG.  3 A  illustrates an example PZR device configuration  300 A with a drive transistor  302  and a sense transistor  304  that share the same well. In the example shown, the drive transistor  302  and sense transistor  304  are npn transistors located in the same p-well of the substrate  310  (e.g., where the substrate  310  is lightly doped). Because both the transistors  302 ,  304  share the same well, the current from the drive signal (V in ) can reach the sense transistor  304  through the substrate, bypassing the desired coupling through the shared gates of the devices, and causing feed-through current (i feed ) from the drive transistor  302  to the sense transistor  304 . This feed-through current can increase the background signal level at the resonance frequency, degrading the true mechanical resonance signal. The amount of feed-through current may be determined by the junction capacitance (C j ) and junction resistance (R j ) of n+/p-well junction and the substrate resistance (R sub ). It is noted that the drive transistor  302  operates in the inversion mode; thus, at high frequencies (e.g., 10&#39;s of GHz or more), the inversion carriers may not respond fast enough, which may limit the operating frequency of the resonator device. 
       FIG.  3 B  illustrates an example PZR device configuration  300 B where the drive transistor  302  and sense transistor  304  are in different wells of opposite polarity. In the example shown, the sense transistor  304  is a npn transistor in the p-well of the substrate  310 , just as in  FIG.  3 A . However, the drive transistor  302  is a pnp transistor in a separate n-well  312  of the substrate  310 . In this configuration, the feed-through current (i feed ) from drive to sense must now go through the junction between the n-well  312  and the pwell of the substrate  310 . Because of this, the feed-through current may be limited by the junction capacitance (C J,sub ) and the junction resistance (R J,sub ) between the wells. Since the junction resistance is usually much larger than the substrate resistance (R sub ,), the feed-through current from the drive transistor  302  to the sense transistor  304  will be reduced. It is noted that the drive transistor  302  operates in the accumulation mode, and accumulation carriers may respond faster to the input frequency compared with inversion carriers. Accordingly, the configuration  300 B may be able to support higher frequencies than the configuration  300 A of  FIG.  3 A . 
     In each of the examples shown, there is a DC voltage source  306  coupled to the gates of both the drive transistor  302  and sense transistor  304 . In addition, there is a DC voltage source  308  coupled to the drain region of the sense transistor  304 , while the source region of the sense transistor  304  is coupled to ground. Further, there is an AC voltage source  309  (e.g., an RF signal source) coupled to the source and drain regions of the drive transistor  302 . The AC signal generated by the AC voltage source may induce a mechanical resonance within the apparatus as described above, and the resonance may cause a modulation of the DC current flowing in the sense transistor  304  (e.g., flowing from the drain region) based on the voltage applied by the DC voltage source  308 . The example configuration shown in  FIG.  3 B  also includes sense circuitry  305  coupled to the sense transistor  304  (e.g., to the drain region of the sense transistor  304 ). The sense circuitry  305  may detect the modulation in the current through the sense transistor  304  caused by the AC input signal applied to the drive transistor. Although not shown, sense circuitry similar to the sense circuitry  305  may be implemented in a similar manner in the example configuration  300 A of  FIG.  3 A . 
     As used herein, a DC contact may refer to a contact that is to be connected to a DC voltage source, such as  308 , and an AC contact may refer to a contact that is to connect to an AC voltage source, such as  309 . In certain embodiments, a DC contact may be shielded by other metal lines connected to a ground to provide DC signal stability (i.e., large capacitance). AC contacts, however, may be moved away and separated from other signals in the device as much as possible (e.g., through signal routing on separate metal layers) to reduce feed-through (providing a small capacitance). To further reduce the capacitance around the AC signal line, ground metal lines nearby or even floating metal strips (e.g., metal fillers) may be further removed from the areas around the AC contacts. 
       FIGS.  4 A- 4 B  illustrate example circuit modeling for the transistor configurations of  FIGS.  3 A- 3 B , respectively. As shown, each drive unit  402  can be modeled by two capacitors (C j , which represents the capacitance of the junction between the source/drain of the drive transistor  302  of  FIG.  3 A  and the substrate  310 , or C j ′, which represents the capacitance of the junction between the source/drain of the drive transistor  302  of  FIG.  3 B  and the well  312 ) in parallel with two resistors (R j , which represents the resistance of the junction between the source/drain of the drive transistor  302  of  FIG.  3 A  and the substrate  310 , or R j ′, which represents the resistance of the junction between the source/drain of the drive transistor  302  of  FIG.  3 B  and the well  312 ), and each sense unit  404  can similarly be modeled by two capacitors (C j , which represents the capacitance of the junction between the source/drain of the sense transistor  304  of  FIGS.  3 A- 3 B  and the substrate  310 ) in parallel with two resistors (R j , which represents the resistance of the junction between the source/drain of the sense transistor  304  of  FIGS.  3 A- 3 B  and the substrate  310 ). 
     In the configuration of  FIG.  3 A , the resistance of the substrate  403  is modeled as R sub  as shown in  FIG.  4 A . In configuration of  FIG.  3 B , the junction between the wells  405  is modeled as follows: the resistance of the substrate and junction between the well of the substrate  310  and the well  312  is modeled as R j,sub  and the capacitance of the junction between the well of the substrate  310  and the well  312  is modeled as C j,sub  as shown in  FIG.  4 B . The behavior of the example RC circuit models shown may then be described as follows. The RC circuit diagram of  FIG.  4 A  may be modeled as: 
     
       
         
           
             
               
                 i 
                 feed 
               
               
                 v 
                 
                   i 
                   ⁢ 
                   n 
                 
               
             
             = 
             
               
                 1 
                 2 
               
               * 
               
                 1 
                 
                   ( 
                   
                     
                       1 
                       
                         
                           
                             2 
                             ⁢ 
                             N 
                           
                           
                             R 
                             j 
                           
                         
                         + 
                         
                           j 
                           ⁢ 
                           ω 
                           ⁢ 
                           2 
                           ⁢ 
                           N 
                           ⁢ 
                           
                             C 
                             j 
                           
                         
                       
                     
                     + 
                     
                       R 
                       
                         s 
                         ⁢ 
                         u 
                         ⁢ 
                         b 
                       
                     
                     + 
                     
                       1 
                       
                         
                           2 
                           
                             R 
                             j 
                           
                         
                         + 
                         
                           j 
                           ⁢ 
                           ω 
                           ⁢ 
                           2 
                           ⁢ 
                           
                             C 
                             j 
                           
                         
                       
                     
                   
                   ) 
                 
               
             
           
         
       
     
     and the RC circuit diagram of  FIG.  4 B  may be modeled as: 
     
       
         
           
             
               
                 i 
                 feed 
               
               
                 v 
                 
                   i 
                   ⁢ 
                   n 
                 
               
             
             = 
             
               
                 1 
                 2 
               
               * 
               
                 1 
                 
                   ( 
                   
                     
                       1 
                       
                         
                           
                             2 
                             ⁢ 
                             N 
                           
                           
                             R 
                             j 
                           
                         
                         + 
                         
                           j 
                           ⁢ 
                           ω2 
                           ⁢ 
                           
                             NC 
                             j 
                             ′ 
                           
                         
                       
                     
                     + 
                     
                       1 
                       
                         
                           1 
                           
                             R 
                             
                               j 
                               , 
                               sub 
                             
                           
                         
                         + 
                         
                           j 
                           ⁢ 
                           ω 
                           ⁢ 
                           
                             C 
                             
                               j 
                               , 
                               sub 
                             
                           
                         
                       
                     
                     + 
                     
                       1 
                       
                         
                           2 
                           
                             R 
                             j 
                           
                         
                         + 
                         
                           j 
                           ⁢ 
                           ω 
                           ⁢ 
                           2 
                           ⁢ 
                           
                             C 
                             j 
                           
                         
                       
                     
                   
                   ) 
                 
               
             
           
         
       
     
     where N refers to the number of drive units in the PZR device (for embodiments with multiple drive units to each sense unit, e.g., as described below), and ω=2πf with f being the frequency. It will be seen from the above equations that the feed-through reduction of the configuration of  FIG.  3 B  becomes more effective when R j  is small, C j  is large, and R sub  is small. 
     Although the examples shown in  FIGS.  3 A- 3 B  include planar transistors, other embodiments may implement different types of transistors, such as FinFET transistors (e.g., as shown in  FIGS.  1 A- 1 B ) or GAA transistors. In addition, in some embodiments, the drive transistor may be implemented as a metal-oxide semiconductor capacitor (MOSCAP). Moreover, in some embodiments, there may be multiple drive transistors/MOSCAPs within the same well (e.g., multiple drive transistors within the well  312 ). 
     Further, though the examples include one drive transistor  302  and one sense transistor  304 , other embodiments may include any suitable number of drive or sense transistors. For example, as described further below, a configuration may include a N:1 drive:sense transistor ratio, where N&gt;1. In particular, N:1 drive:sense ratio configurations, e.g., on the order of 10:1, may be quite beneficial, as shown below. 
       FIGS.  5 A- 5 C  illustrate example PZR devices  500  with different drive:sense ratios in accordance with embodiments of the present disclosure. In particular,  FIGS.  5 A- 5 C  illustrate side cross-sectional views of FinFET-based PZR devices  500 . In each embodiment, there is a sense transistor fin and one or more drive transistor fins on a common substrate  502 , and sharing a common gate  504 . Each sense transistor fin includes a channel  506  surrounded by a dielectric  507  (which is between the channel  506  and the gate  504 ), and each drive transistor fin includes a channel  508  surrounded by a dielectric  509  (which is between the channel  508  and the gate  504 ). The example PZR device  500 A shown in  FIG.  5 A  has a drive:sense ratio of 1, while the example PZR device  500 B shown in  FIG.  5 B  has a drive:sense ratio of 2 and the example PZR device  500 C shown in  FIG.  5 C  has a drive:sense ratio of N. 
       FIGS.  6 A- 6 B  illustrate example simulation data for the transistor configurations shown in  FIGS.  3 A- 3 B . In particular,  FIGS.  6 A- 6 B  illustrate an example numerical simulation of the amount of feed-through as a function of the drive:sense ratios for the configurations of  FIGS.  3 A- 3 B . The simulation data shown is based on the use of tri-gate transistors for a resonant frequency of 10 GHz. As shown in  FIG.  6 B , the percentage decrease in the feed-through of having drive and sense transistors in oppositely-doped wells (e.g., as shown in  FIG.  3 B ) may improve (decrease) the feed-through by more than 20% when compared with the same configuration, but with drive and sense transistors in the same well (e.g., as shown in  FIG.  3 A ). 
       FIG.  7    illustrates an example PZR device  700  with a varactor as a drive circuit in accordance with embodiments of the present disclosure. In particular, the example PZR device  700  includes a drive MOSCAP varactor circuit  702  coupled with a sense transistor  704 , where the drive circuit  702  is in a well of opposite polarity than that of the sense transistor  704 . The drive circuit  702  may enable even higher operating frequencies, as accumulation charge (electrons in this embodiment) may be more effectively supplied by highly-doped contacts. The other elements of the example PZR device  700  are implemented in the same manner as the configuration shown in  FIG.  3 B . Like that configuration, because of the pn junction in the substrate, the PZR device  700  may provide reduced feed-through in a similar manner as described above. 
       FIG.  8    is a block diagram of an example electrical device  800  that may include one or more of the PZR devices disclosed herein. For example, PZR devices of the present disclosure may be utilized in any suitable resonator implementation. For example, the PZR devices of the present disclosure may be implemented in an oscillator of a PLL that is used for clocking purposes (e.g., as PZR device  807  in the oscillator  805  of PLL  803  of processor unit  802  of  FIG.  8   ), as part of an oscillator of a radio frequency (RF) transceiver (e.g., as PZR device  817  in oscillator  815  of the RF transceiver  813  of communication component  812  of  FIG.  8   ), for instance, as part of a local oscillator for heterodyning RF signals or as part of a filter circuit. 
     A number of components are illustrated in  FIG.  8    as included in the electrical device  800 , but any one or more of these components may be omitted or duplicated, as suitable for the application. In some embodiments, some or all of the components included in the electrical device  800  may be attached to one or more motherboards mainboards, or system boards. In some embodiments, one or more of these components are fabricated onto a single system-on-a-chip (SoC) die. 
     Additionally, in various embodiments, the electrical device  800  may not include one or more of the components illustrated in  FIG.  8   , but the electrical device  800  may include interface circuitry for coupling to the one or more components. For example, the electrical device  800  may not include a display device  806 , but may include display device interface circuitry (e.g., a connector and driver circuitry) to which a display device  806  may be coupled. In another set of examples, the electrical device  800  may not include an audio input device  824  or an audio output device  808 , but may include audio input or output device interface circuitry (e.g., connectors and supporting circuitry) to which an audio input device  824  or audio output device  808  may be coupled. 
     The electrical device  800  may include one or more processor units  802 . As used herein, the terms “processor unit”, “processing unit” or “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory. The processor unit  802  may include one or more digital signal processors (DSPs), application-specific integrated circuits (ASICs), central processing units (CPUs), graphics processing units (GPUs), general-purpose GPUs (GPGPUs), accelerated processing units (APUs), field-programmable gate arrays (FPGAs), neural network processing units (NPUs), data processor units (DPUs), accelerators (e.g., graphics accelerator, compression accelerator, artificial intelligence accelerator), controller cryptoprocessors (specialized processors that execute cryptographic algorithms within hardware), server processors, controllers, or any other suitable type of processor units. As such, the processor unit can be referred to as an XPU (or xPU). 
     The electrical device  800  may include a memory  804 , which may itself include one or more memory devices such as volatile memory (e.g., dynamic random access memory (DRAM), static random-access memory (SRAM)), non-volatile memory (e.g., read-only memory (ROM), flash memory, chalcogenide-based phase-change non-voltage memories), solid state memory, and/or a hard drive. In some embodiments, the memory  804  may include memory that is located on the same integrated circuit die as the processor unit  802 . This memory may be used as cache memory (e.g., Level 1 (L1), Level 2 (L2), Level 3 (L3), Level 4 (L4), Last Level Cache (LLC)) and may include embedded dynamic random access memory (eDRAM) or spin transfer torque magnetic random access memory (STT-MRAM). 
     In some embodiments, the electrical device  800  can comprise one or more processor units  802  that are heterogeneous or asymmetric to another processor unit  802  in the electrical device  800 . There can be a variety of differences between the processing units  802  in a system in terms of a spectrum of metrics of merit including architectural, microarchitectural, thermal, power consumption characteristics, and the like. These differences can effectively manifest themselves as asymmetry and heterogeneity among the processor units  802  in the electrical device  800 . 
     In some embodiments, the electrical device  800  may include a communication component  812  (e.g., one or more communication components). For example, the communication component  812  can manage wireless communications for the transfer of data to and from the electrical device  800 . 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 nonsolid medium. The term “wireless” does not imply that the associated devices do not contain any wires, although in some embodiments they might not. 
     The communication component  812  may implement any of a number of wireless standards or protocols, including but not limited to Institute for Electrical and Electronic Engineers (IEEE) standards including Wi-Fi (IEEE 802.11 family), IEEE 802.16 standards (e.g., IEEE 802.16-2005 Amendment), Long-Term Evolution (LTE) project along with any amendments, updates, and/or revisions (e.g., advanced LTE project, ultra mobile broadband (UMB) project (also referred to as “3GPP2”), etc.). IEEE 802.16 compatible Broadband Wireless Access (BWA) networks are generally referred to as WiMAX networks, an acronym that stands for Worldwide Interoperability for Microwave Access, which is a certification mark for products that pass conformity and interoperability tests for the IEEE 802.16 standards. The communication component  812  may operate in accordance with a Global System for Mobile Communication (GSM), General Packet Radio Service (GPRS), Universal Mobile Telecommunications System (UMTS), High Speed Packet Access (HSPA), Evolved HSPA (E-HSPA), or LTE network. The communication component  812  may operate in accordance with Enhanced Data for GSM Evolution (EDGE), GSM EDGE Radio Access Network (GERAN), Universal Terrestrial Radio Access Network (UTRAN), or Evolved UTRAN (E-UTRAN). The communication component  812  may operate in accordance with Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Digital Enhanced Cordless Telecommunications (DECT), Evolution-Data Optimized (EV-DO), and derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. The communication component  812  may operate in accordance with other wireless protocols in other embodiments. The electrical device  800  may include an antenna  822  to facilitate wireless communications and/or to receive other wireless communications (such as AM or FM radio transmissions). 
     In some embodiments, the communication component  812  may manage wired communications, such as electrical, optical, or any other suitable communication protocols (e.g., IEEE 802.3 Ethernet standards). As noted above, the communication component  812  may include multiple communication components. For instance, a first communication component  812  may be dedicated to shorter-range wireless communications such as Wi-Fi or Bluetooth, and a second communication component  812  may be dedicated to longer-range wireless communications such as global positioning system (GPS), EDGE, GPRS, CDMA, WiMAX, LTE, EV-DO, or others. In some embodiments, a first communication component  812  may be dedicated to wireless communications, and a second communication component  812  may be dedicated to wired communications. 
     The electrical device  800  may include battery/power circuitry  814 . The battery/power circuitry  814  may include one or more energy storage devices (e.g., batteries or capacitors) and/or circuitry for coupling components of the electrical device  800  to an energy source separate from the electrical device  800  (e.g., AC line power). 
     The electrical device  800  may include a display device  806  (or corresponding interface circuitry, as discussed above). The display device  806  may include one or more embedded or wired or wirelessly connected external visual indicators, such as a heads-up display, a computer monitor, a projector, a touchscreen display, a liquid crystal display (LCD), a light-emitting diode display, or a flat panel display. 
     The electrical device  800  may include an audio output device  808  (or corresponding interface circuitry, as discussed above). The audio output device  808  may include any embedded or wired or wirelessly connected external device that generates an audible indicator, such speakers, headsets, or earbuds. 
     The electrical device  800  may include an audio input device  824  (or corresponding interface circuitry, as discussed above). The audio input device  824  may include any embedded or wired or wirelessly connected device that generates a signal representative of a sound, such as microphones, microphone arrays, or digital instruments (e.g., instruments having a musical instrument digital interface (MIDI) output). The electrical device  800  may include a Global Navigation Satellite System (GNSS) device  818  (or corresponding interface circuitry, as discussed above), such as a Global Positioning System (GPS) device. The GNSS device  818  may be in communication with a satellite-based system and may determine a geolocation of the electrical device  800  based on information received from one or more GNSS satellites, as known in the art. 
     The electrical device  800  may include an other output device  810  (or corresponding interface circuitry, as discussed above). Examples of the other output device  810  may include an audio codec, a video codec, a printer, a wired or wireless transmitter for providing information to other devices, or an additional storage device. 
     The electrical device  800  may include an other input device  820  (or corresponding interface circuitry, as discussed above). Examples of the other input device  820  may include an accelerometer, a gyroscope, a compass, an image capture device (e.g., monoscopic or stereoscopic camera), a trackball, a trackpad, a touchpad, a keyboard, a cursor control device such as a mouse, a stylus, a touchscreen, proximity sensor, microphone, a bar code reader, a Quick Response (QR) code reader, electrocardiogram (ECG) sensor, PPG (photoplethysmogram) sensor, galvanic skin response sensor, any other sensor, or a radio frequency identification (RFID) reader. 
     The electrical device  800  may have any desired form factor, such as a hand-held or mobile electrical device (e.g., a cell phone, a smart phone, a mobile internet device, a music player, a tablet computer, a laptop computer, a 2-in-1 convertible computer, a portable all-in-one computer, a netbook computer, an ultrabook computer, a personal digital assistant (PDA), an ultra mobile personal computer, a portable gaming console, etc.), a desktop electrical device, a server, a rack-level computing solution (e.g., blade, tray or sled computing systems), a workstation or other networked computing component, a printer, a scanner, a monitor, a set-top box, an entertainment control unit, a stationary gaming console, smart television, a vehicle control unit, a digital camera, a digital video recorder, a wearable electrical device or an embedded computing system (e.g., computing systems that are part of a vehicle, smart home appliance, consumer electronics product or equipment, manufacturing equipment). In some embodiments, the electrical device  800  may be any other electronic device that processes data. In some embodiments, the electrical device  800  may comprise multiple discrete physical components. Given the range of devices that the electrical device  800  can be manifested as in various embodiments, in some embodiments, the electrical device  800  can be referred to as a computing device or a computing system. 
     Some examples of embodiments are provided below. As used in the following examples, the term “connected” may refer to an electrical connection. In some instances, the connection may be a direct connection between two items/components. Further, as used in the following examples, the term “coupled” may refer to a connection that may be direct or indirect. For example, a first component coupled to a second component may include a third component connected between the first and second components. 
     Further, as used herein, the phrase “located on” in the context of a first layer or component located on a second layer or component refers to the first layer or component being directly physically attached to the second part or component (no layers or components between the first and second layers or components) or physically attached to the second layer or component with one or more intervening layers or components. 
     Example 1 includes an apparatus comprising: a first transistor comprising a source region, a drain region, a channel region between the source and drain regions, a gate contact, and a dielectric between the gate contact and the channel region, wherein the source and drain regions of the first transistor are doped regions in a first well; a second transistor comprising a source region, a drain region, a channel region between the source and drain regions, a gate contact, and a dielectric between the gate contact and the channel region, wherein the source and drain regions of the second transistor are doped regions in a second well of opposite polarity than the first well; a first direct current (DC) contact to receive DC current, the first DC contact coupled to the gate contact of the first transistor and to the gate contact of the second transistor; a second direct current (DC) contact to receive DC current, the second DC contact coupled to the drain region of the second transistor; and alternating current (AC) contacts to receive AC current, the AC contacts coupled to the source and drain regions of the first transistor. 
     Example 2 includes the subject matter of Example 1, wherein the source and drain regions of the first transistor are of a different polarity than the first well. 
     Example 3 includes the subject matter of Example 1, wherein the source and drain regions of the first transistor are of the same polarity as the first well. 
     Example 4 includes the subject matter of any one of Examples 1-3, wherein the first and second transistor are planar transistors. 
     Example 5 includes the subject matter of any one of Examples 1-3, wherein the first and second transistor are fin-based field-effect transistors (FinFETs). 
     Example 6 includes the subject matter of any one of Examples 1-5, wherein the second well is a doped substrate, and the first well is a doped region within the substrate. 
     Example 7 includes the subject matter of any one of Examples 1-6, further comprising a third transistor comprising a source region, a drain region, a channel region between the source and drain regions, a gate contact, and a dielectric between the gate contact and the channel region, wherein the source and drain regions of the third transistor are doped regions in a third well of the same polarity as the first well, and the AC contacts are coupled to the source and drain regions of the third transistor. 
     Example 8 includes the subject matter of Example 7, wherein the second transistor is between the first and third transistors. 
     Example 9 includes the subject matter of any one of Examples 1-8, further comprising: a first DC voltage source coupled to the first DC contact; a second DC voltage source coupled to the second DC contact; and an AC voltage source coupled to the AC contacts. 
     Example 10 includes a resonator device comprising: a first transistor comprising a source region, a drain region, a channel region between the source and drain regions, a gate contact, and a dielectric between the gate contact and the channel region, wherein the source and drain regions of the first transistor are doped regions in a first well; a second transistor comprising a source region, a drain region, a channel region between the source and drain regions, a gate contact, and a dielectric between the gate contact and the channel region, wherein the source and drain regions of the second transistor are doped regions in a second well of opposite polarity than the first well; a direct current (DC) source coupled to the gate contact of the first transistor and to the gate contact of the second transistor; an alternating current (AC) source coupled to the source and drain regions of the first transistor; sense circuitry coupled to the second transistor to detect modulation of a current flowing through the second transistor based on an input signal from the AC source. 
     Example 11 includes the subject matter of Example 10, wherein the source and drain regions of the first transistor are of a different polarity than the first well. 
     Example 12 includes the subject matter of Example 10, wherein the source and drain regions of the first transistor are of the same polarity as the first well. 
     Example 13 includes the subject matter of any one of Examples 10-12, wherein the first and second transistor are planar transistors. 
     Example 14 includes the subject matter of any one of Examples 10-12, wherein the first and second transistor are fin-based field-effect transistors (FinFETs). 
     Example 15 includes the subject matter of any one of Examples 10-14, wherein the second well is a doped substrate, and the first well is a doped region within the substrate. 
     Example 16 includes the subject matter of any one of Examples 10-15, further comprising a third transistor comprising a source region, a drain region, a channel region between the source and drain regions, a gate contact, and a dielectric between the gate contact and the channel region, wherein the source and drain regions of the third transistor are doped regions in a third well of the same polarity as the first well, and the AC contacts are coupled to the source and drain regions of the third transistor. 
     Example 17 includes the subject matter of Example 16, wherein the second transistor is between the first and third transistors. 
     Example 18 includes a system comprising: an oscillator comprising a piezoresistive resonator (PZR) apparatus, the PZR apparatus comprising: a sense transistor comprising a source region, a drain region, a channel region between the source and drain regions, a gate contact, and a dielectric between the gate contact and the channel region, wherein the source and drain regions are doped regions in a first well; a plurality of drive transistors, wherein each drive transistor comprises a source region, a drain region, a channel region between the source and drain regions, a gate contact, and a dielectric between the gate contact and the channel region, wherein the source and drain regions of each drive transistor are in a well of opposite polarity than the first well; a first direct current (DC) contact to receive DC current, the first DC contact coupled to the gate contacts of the drive transistors and to the gate contact of the sense transistor; a second direct current (DC) contact to receive DC current, the second DC contact coupled to the drain region of the sense transistor; and alternating current (AC) contacts to receive AC current, the AC contacts coupled to the source and drain regions of the drive transistor; a first DC voltage source coupled to the first DC contact; a second DC voltage source coupled to the second DC contact; and an AC voltage source coupled to the AC contacts. 
     Example 19 includes the subject matter of Example 18, wherein the source and drain regions of the drive transistors are of a different polarity than the first well. 
     Example 20 includes the subject matter of Example 18, wherein the source and drain regions of the drive transistors are of the same polarity as the first well. 
     Example 21 includes the subject matter of any one of Examples 18-20, wherein the drive and sense transistors are planar transistors. 
     Example 22 includes the subject matter of any one of Examples 18-20, wherein the drive and sense transistors are fin-based field-effect transistors (FinFETs). 
     Example 23 includes the subject matter of any one of Examples 18-22, further comprising a phase locked loop (PLL) circuit, wherein the oscillator is in the PLL circuit. 
     Example 24 includes the subject matter of any one of Examples 18-22, further comprising radio frequency (RF) transceiver circuitry, wherein the oscillator is in the RF transceiver circuitry. 
     Example 25 includes an apparatus comprising: a sense transistor comprising a source region, a drain region, a channel region between the source and drain regions, a gate contact, and a dielectric between the gate contact and the channel region, wherein the source and drain regions are doped regions in a first well; a plurality of drive transistors, wherein each drive transistor comprises a source region, a drain region, a channel region between the source and drain regions, a gate contact, and a dielectric between the gate contact and the channel region, wherein the source and drain regions of each drive transistor are in a well of opposite polarity than the first well; a first direct current (DC) contact to receive DC current, the first DC contact coupled to the gate contacts of the drive transistors and to the gate contact of the sense transistor; a second direct current (DC) contact to receive DC current, the second DC contact coupled to the drain region of the sense transistor; and alternating current (AC) contacts to receive AC current, the AC contacts coupled to the source and drain regions of the drive transistor. 
     Example 26 includes the subject matter of Example 25, further comprising: a first DC voltage source coupled to the first DC contact; a second DC voltage source coupled to the second DC contact; and an AC voltage source coupled to the AC contacts. 
     Example 27 includes the subject matter of Example 25, wherein the source and drain regions of the drive transistors are of a different polarity than the first well. 
     Example 28 includes the subject matter of Example 25, wherein the source and drain regions of the drive transistors are of the same polarity as the first well. 
     Example 29 includes the subject matter of any one of Examples 25-28, wherein the drive and sense transistors are planar transistors. 
     Example 30 includes the subject matter of any one of Examples 25-28, wherein the drive and sense transistors are fin-based field-effect transistors (FinFETs). 
     In the foregoing, a detailed description has been given with reference to specific example embodiments. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the disclosure as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense. Furthermore, the foregoing use of embodiment(s) and other exemplarily language does not necessarily refer to the same embodiment or the same example, but may refer to different and distinct embodiments, as well as potentially the same embodiment.