High-efficiency non-sinusoidal bias supply drive

Abstract

In one aspect, a transformer having a primary winding and a secondary winding, the transformer comprises: a plurality of transmission-line cable sections each having at least a first conductor and a second conductor; wherein the first conductors of the transmission-line cable sections are connected in parallel to form the primary winding; and wherein the second conductors of the transmission-line cable sections are connected in series to form the secondary winding. According another aspect, a system for generating bias pulsed waveforms includes: a low-voltage pulse generation stage having an inverter coupled to receive one or more direct current (DC) input voltages; a transformer having a primary winding and a secondary winding; and a controller configured to operate switches of the inverter according to a multi-stage switching sequence to generate bias pulsed waveforms across a primary winding of the transformer.

Description

Docket No.: MIT-662AWO / 25237 HIGH-EFFICIENCY NON-SINUSOIDAL BIAS SUPPLY DRIVE CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. §119 of U.S. Provisional Patent Application No.63 / 594,521 filed on October 31, 2023, which is hereby incorporated by reference herein in its entirety. BACKGROUND

[0002] Radio frequency (RF) power generators are commonly used in semiconductor manufacturing for processes such as plasma etching and plasma-enhanced chemical vapor deposition (PECVD). In plasma etching, ions are accelerated by an electric field posed between electrodes. The accelerated ions are then able to etch a substrate. For PECVD, an RF power source ionizes atoms and molecules, which are able to be deposited in thin films onto a substrate. Both processes are done utilizing one of two types of RF signals. The first is done with a continuous (typically sinusoidal) signal. The amplitude and / or frequency are modulated to vary the output power to the plasma load. This method, however, can result in a broad ion energy distribution function (IEDF), limiting the ability to generate higher-quality etches and film characteristics. The second method utilizes a pulsed RF signal. In this method, output power to the load is controlled via the pulse duty cycle and amplitude. This method narrows the IEDF, enabling increased control over peak ion energy and current. This allows for improved etching and PECVD performance, such as etch feature profiles and film quality.

[0003] Generating bias-pulsed waveforms for plasma-enhanced semiconductor manufacturing processes is challenging as it requires high voltages (exceeding the voltage ratings of off-the-shelf devices), high-frequency operation, and precisely timed waveforms with broad-band frequency content. Different approaches for generating these waveforms for capacitively coupled plasma (CCP) systems have been proposed. One approach is to directly synthesize the pulse from a high-voltage direct current (DC) source using methods such as current and voltage source inverter circuits. These systems can utilize either high- voltage devices or a series stack of many low-voltage devices to meet system voltage requirements. An alternative method would be to use a multi-level inverter structure,Docket No.: MIT-662AWO / 25237 where blocks of sub-circuits are used in combination to reach the desired pulse voltage. These topologies enable the use of low-voltage-rated devices. SUMMARY

[0004] It is appreciated herein that, while these existing methods may enable the use of low-voltage-rated devices, they experience high system complexity, component count, and cost. Therefore, there is a need to develop bias-pulsed waveforms with a simple, compact, and inexpensive approach.

[0005] Disclosed herein are structures and techniques for synthesizing the desired pulsed waveform shape at a convenient voltage and current level and then utilize a transformer to step up the voltage to the desired level. Since the pulsed waveform is an alternating current (AC) signal, it is compliant with the use case of a magnetic transformer. Disclosed systems enable the use of fewer low-voltage devices while reducing system cost and complexity.

[0006] According to one aspect of the present disclosure, a transformer having a primary winding and a secondary winding comprises: a plurality of transmission-line cable sections each having at least a first conductor and a second conductor; wherein the first conductors of the transmission-line cable sections are connected in parallel to form the primary winding; and wherein the second conductors of the transmission-line cable sections are connected in series to form the secondary winding.

[0007] In some embodiments, the plurality of transmission-line cable sections comprises M transmission-line cable sections; the primary winding has N turns; and the secondary winding has N x M turns. In some embodiments, the transformer comprises a step-up transformer with a turn ratio of N to N x M. In some embodiments, different ones of the plurality of transmission-line cable sections have different insulation thicknesses. In some embodiments, the plurality of transmission-line cable sections comprise a plurality of coaxial cable sections. In some embodiments, either the first conductor or the second conductor of the plurality of transmission-line cable sections comprise Litz wire. In some embodiments, both the first conductor and the second conductor of plurality of transmission-line cable sections comprise Litz wire.Docket No.: MIT-662AWO / 25237

[0008] In some embodiments, the transformer further comprises a bobbin having: a central opening shaped to fit around a leg of the transformer; and a plurality of spacers arranged around the central opening and configured to position the primary and secondary windings. In some embodiments, the central opening has a rectangular shape, wherein the plurality of spacers include at least four pluralities of spacers, each of the at least four pluralities of spacers arranged in a vertical stack along a different side of the central opening. In some embodiments, the bobbin is comprised of a material having a dielectric constant equal to or greater than a dielectric constant of air. In some embodiments, the bobbin is comprised of at least one of: polylactic acid (PLA); acrylonitrile butadiene styrene (ABS); polyether ether ketone (PEEK); and polyetherimide (PEI). In some embodiments, the bobbin is 3D printed.

[0009] According to one aspect of the present disclosure, a transformer having a primary winding and a secondary winding comprises: a plurality of bifilar transmission line cables each having a first section and a second section; wherein the first sections the bifilar transmission line cables are connected in parallel to form the primary winding; and wherein the second sections of bifilar transmission line cables are connected in series to form the secondary winding. In some embodiments, the plurality of bifilar transmission line cables comprises M of bifilar transmission line cables; the primary winding has N turns; and the secondary winding has N x M turns. In some embodiments, the bifilar transmission line cables comprise Litz wire.

[0010] According to one aspect of the present disclosure, a system for generating bias pulsed waveforms comprises: a low-voltage pulse generation stage having a plurality of switches to form an inverter, the low-voltage pulse generation stage coupled to receive one or more direct current (DC) input voltages; a transformer having a primary winding and a secondary winding; and a controller configured to operate the switches of the low-voltage pulse generation stage according to a multi-stage switching sequence to generate a low- voltage signal having a bias pulsed waveform across the primary winding of the transformer, the low-voltage signal stepped up from the primary winding to the secondary winding of the transformer to provide a high-voltage output pulse.Docket No.: MIT-662AWO / 25237

[0011] In some embodiments, the system further comprises a capacitively coupled plasma (CCP) apparatus coupled to receive the high-voltage output pulse. In some embodiments, the plurality of switches includes at least two switches, wherein the controller is configured to control the at least two switches alternately. In some embodiments, the transformer comprises as an auto-transformer. In some embodiments, the system is configured to achieve zero-voltage switching (ZVS). BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The manner of making and using the disclosed subject matter may be appreciated by reference to the detailed description in connection with the drawings, in which like reference numerals identify like elements.

[0013] Fig.1 is a schematic diagram showing a circuit for generating bias pulsed waveforms, according to some embodiments.

[0014] Fig.2A and 2B are schematic diagrams showing alternating current (AC) equivalent models of a bias pulsed generation circuit, according to some embodiments.

[0015] Fig.3 is a graphical diagram showing relative waveforms of a bias pulse generating circuit, according to some embodiments.

[0016] Fig.4 is a schematic diagram showing a circuit for slew rate variable inductance.

[0017] Fig.5 is a diagram showing multiple sections of coaxial cable connected for use as transformer windings, according to some embodiments.

[0018] Fig.6 is a diagram showing coaxial cable windings on a section of core for use as a transformer, according to some embodiments.

[0019] Fig.7 is a diagram showing bifilar transmission line cable windings core for use as a transformer, according to some embodiments.

[0020] Fig.8 shows an example of bobbin that can be used on a center post of a transformer core, according to some embodiments.Docket No.: MIT-662AWO / 25237

[0021] Fig.9 is a block diagram showing an example of a system for generating bias pulsed waveforms, according to some embodiments.

[0022] The drawings are not necessarily to scale, or inclusive of all elements of a system, emphasis instead generally being placed upon illustrating the concepts, structures, and techniques sought to be protected herein. DETAILED DESCRIPTION

[0023] Turning to Fig. 1, an illustrative circuit 100 for generating bias pulsed waveforms includes a low-voltage pulse generation stage, an auto-transformer, and a capacitively coupled plasma (CCP) load model.

[0024] In the example shown, the low-voltage pulse generation stage comprises two branches. A first (or “top”) branch has a first switch 104a (^^), a first diode 106a (^^), and a first capacitor 108a (^^), all connected in parallel to a first input voltage 102a (^^). A second (or “bottom”) branch has a second switch 104b (^^), a second diode 106b (^^), and a second capacitor 108b (^^), all connected in parallel to a second input voltage 102b (^^). The input voltages 102a, 102b can be provided as DC voltage sources and connected to a ground node 109, as shown. The auto-transformer has a primary winding with ^^turns represented by a primary inductive element 110a (^^) with ^^turns, a magnetizing inductance 110b (^^), and a secondary winding with ^^turns represented by secondary inductive element 110c (^^). The CCP load is modeled by a capacitive element 112 (^^^^^^^) and a resistive element 114 (^^^^^^^).

[0025] Pulse generation can be achieved by controlling switches ^^and ^^alternately, to generate a bipolar waveform across the primary winding of the transformer. For example, as shown in Fig.1, the switch network can synthesize a pulse voltage ^^at a node 116 and across primary winding 110a.

[0026] A dead time between switching can be allocated to set the slew rate of the pulsed signal. The transformer can have a set magnetizing inductance (^^) that is utilized to achieve zero-voltage switching (ZVS). The pulsed signal is then stepped up from theDocket No.: MIT-662AWO / 25237 primary winding (^^) to the secondary winding (^^) of the transformer (which can be an auto-transformer). This output pulse is applied across the CCP system.

[0027] A CCP system can be modeled as a series RC branch, as shown in Fig.1. When a bias voltage is applied to electrodes in a plasma chamber, ions and electrons begin to move in opposite directions. This generates regions in the chamber: a bulk plasma region, where the quantity of positively charged ions and electrons is equal, giving the region a net zero potential, and a sheath region surrounding the bulk plasma, in which the quantity of electrons outnumbers the ions. A potential is generated within the sheath, represented by a capacitive element 112 (^^^^^^^). A resistive element 114 (^^^^^^^) represents the load element of the plasma that sets the output power. In typical CCP systems, the real power portion of the system is significantly smaller than the reactive power, so ^^^^^^^is negligible compared to the impedance of ^^^^^^^.

[0028] While switches 104a, 104b are illustrated as n-type field effect transistors (NFETs), other types of switches may be used, including but not limited to field effect transistors (FETs) and metal oxide semiconductor field effect transistors (MOSFETs).

[0029] Figs.2A and 2B show alternating current (AC) equivalent models of a bias pulsed generation circuit (e.g., the circuit of Fig.1 or a similar circuit). These models are useful for understanding, analyzing, and implementing the general concepts sought to be protected herein. Like elements of Figs. 1, 2A, and 2B are shown using like reference numerals.

[0030] Fig.2A shows an equivalent model 200 including scaled load and switch capacitance in parallel with the magnetizing inductance. From an AC perspective, the switch capacitances (^^and ^^) look as though they are in parallel to the magnetizing inductance. The plasma load is reflected to the primary of the transformer by the primary to secondary turns ratio (^^:^^= 1:^) so that ^^^^^^^,^^= ^^^^^^^^^and ^^^^^^^,^^= ^^^^^^^^^^.

[0031] Fig.2B shows a reduced equivalent model 240 with signal equivalent capacitance. As shown, the model can be further simplified by calculating the equivalentDocket No.: MIT-662AWO / 25237 capacitance of ^^, ^^, and ^^^^^^^,^^in parallel. The equivalent capacitance is represented by capacitive element 142 (^^^). Since the resistance of the plasma is negligible compared to the impedance of ^^^^^^^, it can be excluded from the model.

[0032] Fig.3 shows a relative output voltage waveform 302 on a first graph 300a and a relative magnetizing inductor current waveform 304 on a second graph 300b that may result from the switches 104a, 104b operating alternately. The graphs 302a, 302b share a common time axis (^). The dead time is dictated either by turning both switches off or by the switch diode. In the example of Fig.3, four stages of circuit operation 306a–d (stage 1–4) are shown. Also shown are reference currents 308a, 308b, 308c, 308d (^^, ^^, −^^, −^^). Table 1 Stage 1 2 3 4 ^^ ^^−^^^^^(^^^) + ^^^^^(^^^)−^^ ^^^^^(^ ^) − ^ ^^^(^ ^) ^^ ^ ^ ^ ^^^^^ ^ ^^^^^^^^ − ^^^^^^^(^^^) + ^^^^^^^^^^(^^^)−^^^ + ^^−^^^^^(^^^) − ^^^^^^^^^^(^^^)^^^^

[0033] Table 1 gives bias pulse generator circuit equations (output voltage and inductor current equations) for pulsed waveform voltage and inductor current, where ^^= ^ ^^^^^^. The circuit operation is as follows: During stage 1, switch ^^is maintained on until ^ reaches the r^^eference current ^^(switch ^^is off). voltage ^^is clamped to the top supply DC voltage source ^^. At this point, the switch ^^is turned off, beginning stage 2, and the current ^^^begins to flow through ^^^. Thisthe voltage across the switch ^^to rise in a resonant manner, ensuring ZVS turn-off. The output voltage decreases from ^^until it reaches −^^, at which point the bottom switch diode ^^clamps ^^to the bottom supply voltage, beginning stage 3. During the time when diode ^^is conducting, the switch ^^is able to turn on with ZVS turn-on. Switch ^^remains on for a controlled time or until ^^^reaches the reference current −^^, at which point switch ^^Docket No.: MIT-662AWO / 25237 turns off with ZVS turn-off, beginning stage 4. The voltage rises until it reaches ^^, turning on the diode ^^, allowing ^^to turn on with ZVS turn-on.

[0034] Thismodeled in Figs. 2A and 2B is capable of generating pulses at any duty cycle by varying the value of the input voltages so that the volts-seconds balance overthe magnetizing inductance is maintained. The equation for the volts-seconds balance is:0= ^^^^ − ^^^^ + ^^^^^^^^ ^^^(^^^^) − ^^^^^^^^ ^^^(^^^^) +^^^^ ^^ ^^ (1)where ^ is thetop voltage source ^^, ^^is the time for which the voltage of the magnetizing inductor is clamped to the bottom voltage source −^^, and ^^is the time when the pulse is rising or falling. Thus, given times ^^, ^^, and ^^, the voltage sources ^^and ^^may be adjusted to maintain the volts-seconds balance.

[0035] The value of ^^may be selected such that it can properly drive the slew rate of the pulsed voltage asas be of sufficient magnitude to enable ZVS. If ^^, ^^, ^^, and ^^are given, ^^and ^^are found explicitly using the system of equations outlined in equation. ì^^= 1 / ^^^^^^(2)

[0036] The required values for ^^and ^^can be approximated more simply if the pulsed waveform is approximatedtrapezoidal. ^^,^^^^^^= ^^^^^^^^^^^^(3)

[0037] Even with significantthat were not accounted for in the selection of the DC voltage sources and magnetizingDocket No.: MIT-662AWO / 25237 inductance that causes the volts-seconds balance to become unsatisfied. This can be rectified by placing a DC-blocking capacitor in series with one of the voltage sources or with the transformer primary. Excess energy in the magnetizing inductor can charge this capacitor to a voltage such that the volts-seconds balance on the inductor is again satisfied.

[0038] Turning to Fig. 4, the slew rate of the pulsed voltage waveform can be adjusted on the fly by modulating the effective magnetizing inductance. In some embodiments, this can be achieved by placing external inductors in parallel with the transformer. Placing a switch between the transformer and a single external inductor provides two choices for the value of effective magnetizing inductance, and thus allows for two selections for slew rate. In some embodiments, a bank of inductors external can be used such that any combinationof parallel inductors is selectable. In this case, the number of slew rate options grows to:2^, where ^ is the number of external inductors (4)

[0039] Fig.4 shows an illustrative circuit 400 with n inductors 402a–n (^^–^) each connected in series with a respective switch 404a–n, and in parallel with the primary winding 110a of a transformer, such that the net magnetizing inductance of the transformer can be set by some parallel combination of the inductors 402a–n.

[0040] In some embodiments, a single variable inductor in parallel with the transformer may be used.

[0041] Another option is to vary the equivalent capacitance of the system by adding external capacitance in parallel with the transformer. This can be achieved, for example, with a multiplexed capacitor bank, similar to that described for the inductor, or via a variable capacitor.

[0042] Turning to Figs.5–7, as previously discussed, a circuit (e.g., a circuit as in Fig. 1, 2A, and / or 2B) can include a transformer to scale a pulse voltage ^^synthesized by a switch network. One challenge is realizing a transformer that can provide scaling with sufficient fidelity across a wide frequency bandwidth comprised within a pulsed waveform. Thus, it may be desirable to design transformers minimizing parasitic that interfere with the synthesis of these pulsed waveforms, especially as relates to the leakage inductance(s) of the transformer. The transformation can be realized with a conventionalDocket No.: MIT-662AWO / 25237 transformer, an auto-transformer, or a transmission line transformer. An auto-transformer is advantageous as the pulsed output voltage can be scaled by the sum of primary and secondary turns (^^= ^^(^^+ ^^) / (^^)), providing additional voltage gain than a traditional transformer. A transmission line transformer, such as a Ruthroff transformer, is advantageous as it allows for broadband transformation due to its ability to operate in “transmission line mode” at higher frequencies.

[0043] To reduce transformer leakage inductance, a transformer can be provided that has the minimum (or near minimum) leakage fields between primary and secondary winding segments, even at the expense of primary-to-secondary capacitance between the winding segments. This can be achieved by minimizing the spacing between primary and secondary conductors while respecting the voltage breakdown requirements of that section of the conductor, and by carefully organizing the structure of the primary and secondary windings. Thus, in some embodiments, different portions of the primary and secondary windings can have different degrees of insulation. One means of organizing the windings is to use a coaxial arrangement of primary and secondary conductors separated by dielectric insulation, such as constructed with coaxial transmission-line cabling.

[0044] According to embodiments of the present disclosure, portions of the coaxial cable for the transformer may have different insulation spacing (and characteristic impedance and voltage breakdown limits). By doing so, leakage inductance posed by the overall transformer structure can be reduced from the case where all of the coaxial conductors have identical characteristics and higher performance can thereby be achieved.

[0045] In using coaxial conductors, or other transmission-line arrangements of conductor, both controlled distributed leakage and controlled distributed capacitance may be achieved, which can provide transmission-line propagation on a conductor segment. Notably, the leakage is known: it is the distributed inductance of the transmission line posed by the cabling section. The distributed nature of the inductance and capacitance can aid in achieving high bandwidth. However, more broadly than conceived for conventional transmission-line transformers, transmission-line structures may be employed for windings on designs in which magnetic induction is a major source of voltage gain, as in conventional transformers and auto-transformers.Docket No.: MIT-662AWO / 25237

[0046] One of the conductors of a transmission line section can be used as the primary side winding and the other as the secondary side winding. When a turns ratio larger than 1 is needed, multiple transmission line sections may be used, connected with one conductor from each section connected in parallel to form the primary windings and the other conductors in each section connected in series to form the secondary winding. In some embodiments, the different transmission-line sections may have different insulation capabilities and characteristic impedance.

[0047] One such implementation 500 is illustrated in Fig.5, where multiple sections 502a–c (502 generally) of coaxial cable are connected for use as transformer windings. The outer conductors of the coaxial cables act as the primary (^^), and the outer conductors of the multiple sections 502 can be connected in parallel, as shown. The inner conductors of the coaxial cables act as the secondary (^^), and the inner conductors of the multiple sections 502 can be connected in series, as also shown. While the embodiment of Fig. 5 shows three sections 502a–c, other numbers of sections can be used in other embodiments.

[0048] Fig.6 shows coaxial cable windings 602a–c on a section of core 600, with two (2) primary winding turns of three parallel outer conductors and six (6) secondary winding turns of three series inner conductors. Windings 602a–c shown in Fig.6 may correspond to sections 502a–c, respectively, of Fig. 5.

[0049] The distributed inductance is defined by the geometry of the transmission line. To reduce the distributed inductance, the distance between the two conductors is often reduced. Reducing this distance means reducing the thickness of the insulation, which often means reducing the allowable voltage difference between the two conductors.

[0050] In order to reduce, and ideally minimize, distributed inductance across the entire winding, a tapered approach may be used in some embodiments. Multiple sections of the transmission line are used, as described above. Each section of coaxial cable can be individualized such that it has the lowest possible distributed inductance given the potential difference between the conductors. In this tapered structure, portions of the transformer that have a lower voltage difference may use a smaller cable (with lessDocket No.: MIT-662AWO / 25237 insulation). This means that these sections have lower distributed inductance and thus lower leakage inductance. Less insulation also typically indicates a smaller cable diameter, so the winding uses less window area. Using this approach, a transformer can be optimized to have the lowest leakage and size possible. For example, as shown in Fig.6, the thickness of insulation 604c in winding 602c may be less than that of insulation 604b in winding 602b, while the thickness of insulation 604a in winding 602a may be less than that of insulation 604c.

[0051] It will be recognized that while this concept is illustrated with coaxial arrangements of conductors, other arrangements can likewise be used, such as bifilar (or higher multifilar) conductor sets, or other multi-conductor transmission-line structures that are known.

[0052] Fig.7 shows two bifilar transmission line cable windings 702a, 702b on a section of core 700, with two (2) primary winding turns of two parallel conductors, one from each section of transmission line, and four (4) secondary winding turns of two series conductors, one from each section of transmission line.

[0053] In some embodiments, transmission lines can be constructed out of Litz wire in order to reduce high frequency copper loss. In the case of coaxial, transmission line structure can use a Litz wire for an inner conductor, and a copper shield or Litz wound outer conductor. In the case of bifilar or multifilar, transmission lines can be implemented with a standard Litz wire structure for each conductor.

[0054] In some embodiments, alternative transmission line constructions can similarly be optimized to achieve low leakage inductance, such as the “two-wire line", “parallel- plate line" and “strip line" constructions. Their distributed inductance can be decreased through variations in the geometric construction of the transmission line, making these constructions candidates for low-leakage transformers.

[0055] The transformer structures illustrated and described with Figs.5–7 can be used within, but are not limited to use within, a circuit for generating bias pulsed waveforms, such as the circuit of Fig.1. Transformer structures disclosed herein may be used in various other circuits, systems, and applications.Docket No.: MIT-662AWO / 25237

[0056] Turning to Fig. 8, to generate ideal, predictable bias pulsed waveforms, it is important to consider the transformer parasitics in calculations. To facilitate the co-design process of the inverter, transformer, and controls, it is important to discern the transformer parasitic prior to construction. This also facilitates the construction of repeatable devices. These parasitics include the transformer leakage inductance, the primary-to-secondary winding capacitance, and the turn-to-turn capacitance.

[0057] By constructing the transformer windings from transmission lines, such as coaxial cables, the leakage inductance, and primary-to-secondary winding capacitance are defined by the transmission line geometry. They are the distributed inductance and distributed capacitance of the cable, respectively.

[0058] The turn-to-turn capacitance can also be described as a distributed capacitance if the spacing between each turn is precisely equal. A simple method to implement this is to use a winding bobbin with spacers between turns. The bobbin should serve to secure the windings in a precise location. An example of this is depicted in Fig.8. More generally, the bobbin can be designed to provide repeatable parasitics and voltage stresses within the transformer by repeatably positioning the windings.

[0059] Fig.8 shows an example of a bobbin 800 that can be used on the center post of a transformer core. The illustrative bobbin 800 includes spacers 802a, 802b, etc. (802 generally) through which the windings (e.g., windings similar to those illustrated in Figs. 6 and 7) can be placed to ensure desired positioning. Bobbin 800 also includes a central opening 804 (extending from top to bottom) which can be shaped to fit around the center post. In the example of Fig. 8, central opening 804 has a rectangular (or rounded rectangular) shape, and a plurality of spacers 802 can be formed in a vertically stack on each of the four sides of central opening 804. The length 806l, width 806w, and height 806h of a given spacer 802 may be selected based on the number of coaxial cables, diameter of the coaxial cables, the number of windings, and / or other factors.

[0060] In some embodiments, bobbin 800 can be manufactured using 3D-printing technology. A wide range of easily 3D-printed materials can be employed for this purpose. For a given design, a material, infill density, and printing pattern that provides sufficientDocket No.: MIT-662AWO / 25237 turn-to-turn insulation should be selected. Common materials such as polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) will have dielectric constants slightly higher than that of air. Materials such as polyether ether ketone (PEEK) and polyetherimide (PEI, branded as ULTEM) may also be desirable in this application. In some cases, bobbin 800 can also be used as a form to repeatedly pot the windings.

[0061] Fig.9 shows an example of a system 900 for generating bias pulsed waveforms, according to some embodiments. The illustrative system 900 includes a low- voltage DC source 902, a biased pulse waveform generator 904, and a controller 906. Waveform generator 904—which may be implemented using any of the biased pulse waveform generation circuits / models described above including but not limited to circuit 100 of Fig.1—receives low-voltage DC from source 902 and provides RF power to a load 908 (e.g., a CCP system, device, apparatus, etc.). Controller 906 may generate control signals to operate one or more switches of waveform generator 904 according to a multi- stage switching sequence such as described above.

[0062] As used herein, the terms “processor” and “controller” are used to describe electronic circuitry that performs a function, an operation, or a sequence of operations. The function, operation, or sequence of operations can be hard coded into the electronic circuit or soft coded by way of instructions held in a memory device. The function, operation, or sequence of operations can be performed using digital values or using analog signals. In some embodiments, the processor or controller can be embodied in an application specific integrated circuit (ASIC), which can be an analog ASIC or a digital ASIC, in a microprocessor with associated program memory, in a digital signal processor (DSP), and / or in a discrete electronic circuit, which can be analog or digital. A processor or controller can include internal processors or modules that perform portions of the function, operation, or sequence of operations. Similarly, a module can include internal processors or internal modules that perform portions of the function, operation, or sequence of operations of the module.

[0063] As used herein, the term “predetermined,” when referring to a value or signal, is used to refer to a value or signal that is set, or fixed, in the factory at the time of manufacture, or by external means, e.g., programming, thereafter. As used herein, the termDocket No.: MIT-662AWO / 25237 “determined,” when referring to a value or signal, is used to refer to a value or signal that is identified by a circuit during operation, after manufacture.

[0064] While electronic circuits shown in figures herein may be shown in the form of analog blocks or digital blocks, it will be understood that the analog blocks can be replaced by digital blocks that perform the same or similar functions and the digital blocks can be replaced by analog blocks that perform the same or similar functions. Analog-to- digital or digital-to-analog conversions may not be explicitly shown in the figures but should be understood.

[0065] In the foregoing detailed description, various features are grouped together in one or more individual embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that each claim requires more features than are expressly recited therein. Rather, inventive aspects may lie in less than all features of each disclosed embodiment.

[0066] References in the disclosure to “one embodiment,” “an embodiment,” “some embodiments,” or variants of such phrases indicate that the embodiment(s) described can include a particular feature, structure, or characteristic, but every embodiment can include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment(s). Further, when a particular feature, structure, or characteristic is described in connection knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0067] The disclosed subject matter is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The disclosed subject matter is capable of other embodiments and of being practiced and carried out in various ways. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the disclosed subject matter. Therefore,Docket No.: MIT-662AWO / 25237 the claims should be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the disclosed subject matter.

[0068] Although the disclosed subject matter has been described and illustrated in the foregoing exemplary embodiments, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the details of implementation of the disclosed subject matter may be made without departing from the spirit and scope of the disclosed subject matter.

[0069] All publications and references cited herein are expressly incorporated herein by reference in their entirety.

Claims

Docket No.: MIT-662AWO / 25237 CLAIMS 1. A transformer having a primary winding and a secondary winding, the transformer comprising: a plurality of transmission-line cable sections each having at least a first conductor and a second conductor; wherein the first conductors of the transmission-line cable sections are connected in parallel to form the primary winding; and wherein the second conductors of the transmission-line cable sections are connected in series to form the secondary winding.

2. The transformer of claim 1 wherein: the plurality of transmission-line cable sections comprises M transmission-line cable sections; the primary winding has N turns; and the secondary winding has N x M turns.

3. The transformer of claim 2 wherein the transformer comprises a step-up transformer with a turn ratio of N to N x M.

4. The transformer of claim 1 wherein different ones of the plurality of transmission- line cable sections have different insulation thicknesses.

5. The transformer of claim 1 wherein the plurality of transmission-line cable sections comprise a plurality of coaxial cable sections.

6. The transformer of claim 1 wherein either the first conductor or the second conductor of the plurality of transmission-line cable sections comprise Litz wire.Docket No.: MIT-662AWO / 25237 7. The transformer of claim 1 wherein both the first conductor and the second conductor of plurality of transmission-line cable sections comprise Litz wire.

8. The transformer of claim 1 further comprising a bobbin having: a central opening shaped to fit around a leg of the transformer; and a plurality of spacers arranged around the central opening and configured to position the primary and secondary windings.

9. The transformer of claim 8 wherein the central opening has a rectangular shape, wherein the plurality of spacers include at least four pluralities of spacers, each of the at least four pluralities of spacers arranged in a vertical stack along a different side of the central opening.

10. The transformer of claim 8 wherein the bobbin is comprised of a material having a dielectric constant equal to or greater than a dielectric constant of air.

11. The transformer of claim 8 wherein the bobbin is comprised of at least one of: polylactic acid (PLA); acrylonitrile butadiene styrene (ABS); polyether ether ketone (PEEK); and polyetherimide (PEI).

12. The transformer of claim 8 wherein the bobbin is 3D printed.

13. A transformer having a primary winding and a secondary winding, the transformer comprising: a plurality of bifilar transmission line cables each having a first section and a second section;Docket No.: MIT-662AWO / 25237 wherein the first sections the bifilar transmission line cables are connected in parallel to form the primary winding; and wherein the second sections of bifilar transmission line cables are connected in series to form the secondary winding.

14. The transformer of claim 13 wherein: the plurality of bifilar transmission line cables comprises M of bifilar transmission line cables; the primary winding has N turns; and the secondary winding has N x M turns.

15. The transformer of claim 13 wherein the bifilar transmission line cables comprise Litz wire.

16. A system for generating bias pulsed waveforms, the system comprising: a low-voltage pulse generation stage having a plurality of switches to form an inverter, the low-voltage pulse generation stage coupled to receive one or more direct current (DC) input voltages; a transformer having a primary winding and a secondary winding; and a controller configured to operate the switches of the low-voltage pulse generation stage according to a multi-stage switching sequence to generate a low-voltage signal having a bias pulsed waveform across the primary winding of the transformer, the low-voltage signal stepped up from the primary winding to the secondary winding of the transformer to provide a high-voltage output pulse.

17. The system of claim 16 further comprising a capacitively coupled plasma (CCP) apparatus coupled to receive the high-voltage output pulse.Docket No.: MIT-662AWO / 25237 18. The system of claim 16 wherein the plurality of switches includes at least two switches, wherein the controller is configured to control the at least two switches alternately.

19. The system of claim 18 wherein the transformer comprises as an auto-transformer.

20. The system of claim 18 configured to achieve zero-voltage switching (ZVS).

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