PRIORITY CLAIM

Not applicable.

CROSS-REFERENCE TO RELATED ARTICLES

1. “Load Pull” [online] Wikipedia, [Retrieved on 2017 Aug. 24]. Retrieved from Internet <URL: https://en.wikipedia.org/wiki/Load_pull>.2. “Computer Controlled Microwave Tuner, CCMT”, Product Note 41, Focus Microwaves Inc. 1998, pages 2-4.3. “Standing wave ratio” [online], Wikipedia, [Retrieved on 2017 Feb. 3]. Retrieved from Internet <URL: https://en.wikipedia.org/wiki/Standing_wave_ratio>.4. Tsironis, U.S. Pat. No. 6,674,293, “Adaptable pre-matched tuner system and method”.5. “MPT, a universal Multi-Purpose Tuner”, Product Note 79, Focus Microwaves Inc., October 2004.6. “On Wafer Load Pull Tuner Setups: A Design Help”, Application Note 48, Focus Microwaves, December 2001, page 2 ff., FIG. 2.7. “ACP40-GSG-xxx Probes”, Brochure PN 153-231-B [online], FormFactor [Retrieved on 2021 Apr. 14]. Retrieved from Internet <URL:https://formfactor.com/download/acp-quick-guide/?/wpdmdl=3524&refresh=60764fb91b8a31618366393)>.8. Load Pull Characterization, White Paper #64, Focus Microwaves Inc., Chapter 2, pp. 13-15, Chapter 9, pp. 43-49.9. Tsironis, C. U.S. Pat. No. 10,686,239, “Slide screw tuners with offset tuning probes and method”, FIGS. 10, 12.10. Tsironis, C. U.S. Pat. No. 9,335,345, “A Method for Planarity Alignment of Waveguide Wafer Probes”.11. Tsironis, C. U.S. Pat. No. 9,653,332, “Wafer probe holder for planarity and orientation adjustment”, FIG. 3.

BACKGROUND OF THE INVENTION

This invention relates to load and source pull testing of low noise and medium and high-power RF transistor and amplifiers chips on semiconductor wafers using remotely controlled electro-mechanical impedance tuners.

Modern design of low noise and high-power RF amplifiers used in various communication systems, requires accurate knowledge of the active device's (transistor's) characteristics. In such circuits, it is insufficient for the transistors, which operate in their low noise or highly non-linear regime, close to power saturation, to be described using noise or non-linear numeric models only.

A popular method for testing and characterizing such high-power microwave and millimeter-wave transistors (DUT, device under test) is “load pull” (FIG. 1). Low noise transistors are tested using “source pull”. Load or source pull is a measurement technique employing impedance tuners2,4and other test equipment, such as signal or noise sources1, test fixtures housing a DUT3, and power meters or low noise receivers5, the whole controlled by a computer6; the computer controls and communicates with the tuners2,4and the other equipment1,5using digital cables7,8,9. The tuners are used in order to manipulate the microwave impedance conditions in a systematic and controlled manner under which the DUT is tested (see ref. 1); impedance tuners allow determining the optimum impedance conditions for designing amplifiers and other microwave components for specific performance targets, such as noise parameters, gain, efficiency, inter-modulation etc. for devices in chip-form preferably on-wafer (see ref. 6).

Impedance tuners (FIG. 3and ref. 2 and 9) use, in general, the slide-screw concept, wherein one or more adjustable tuning probes33(see ref. 4 and 5) are inserted in a slotted transmission airline (slabline)32having two sidewalls, a test port36and an idle port, a center conductor34(see ref. 4 andFIG. 5); the tuning probe (slug)33is attached to a precision vertical axis31, which is mounted in a mobile carriage38, using an extension bracket35; the axis31, controlled by motor39can move the probe33vertically in Y direction, starting at the top and moving towards the center conductor34; the carriage38can move the probe33horizontally (in X direction) either towards or away from the test port36(and the DUT, which is attached to the test port) parallel to the center conductor34. The vertical movement Y changes the amplitude of the reflection factor α, seen at the tuner test port36, whereas the horizontal movement X changes its phase. This way a large portion of the Smith chart (FIG. 2) is covered, and the high movement resolution of the control mechanics allows synthesizing a large number of impedances from a minimum complex impedance Zmin to a maximum Zmax at any given frequency within the “tuning and frequency range” of the tuner. Typical values of state-of-the-art tuners are Real(Zmin)=2Ω and Real(Zmax)=1250Ω; this corresponds to a Voltage Standing Wave Ratio (VSWR) of 25:1 (see ref. 3). The relation between reflection factor Γ and impedance Z is given by
Γ=|Γ|*exp(jφ)=(Z−Zo)/(Z+Zo)  {eq.1},
wherein Z is the complex impedance Z=R+jX and Zo is the characteristic impedance (typically 50 Ohm). |Γ| varies between 0 and 1; the intrinsic 22 tuning range |Γmax| of the tuner is reduced to the effective 23 tuning range ΓDUTat the DUT reference plane by the insertion loss10,11between the tuner and the DUT (FIGS. 1, 2 and 5).

To minimize this insertion loss two prior art methods (see ref. 8 pages 32-33 and ref. 9) have been employed: (a) moving the tuning probe33as close to the tuner test port36as much as physically possible, and (b) eliminating the RF cable (FIGS. 5 and 13) by tilting and connecting the tuner directly to the wafer probe (FIGS. 8-10). To be able to move the tuner body close to the wafer probe and thus eliminating the RF cable (FIG. 5) one needs to reduce the tuner profile (FIG. 8). One way for doing this has been described in ref. 9. Herein the vertical stepper motor39has been moved behind the carriage38and the slabline32has been attached externally protruding towards the DUT. A realistic view of the low-profile tuner is shown inFIG. 4. For practical reasons the housing37has been redesigned to include and protect the protruding slabline32as shown inFIG. 8.

However, if the wafer-probe (see ref. 7) is connected to the tuner simply by directly joining the coaxial connector61of the probe with the coaxial adapter92of the tuner test port, as depicted inFIG. 16Aand (FIG. 10 or 12 of ref. 9), then (a) the joining is not going to be secured and (b) planarity adjustment (FIGS. 7A and 7B) is uncontrollable and possible only by feeling the tightening torque applied by hand between the two connectors. A secure method for controlling the planarity is commercially available (FIGS. 13, 16, 17), however, it is cumbersome and requires a lossy RF cable to connect to the tuner (FIGS. 5, 13, 17A), creating this way an insertion loss10,11and a reduction of the tuning range (FIG. 2). The optimum overall solution is, therefore, a low-profile tuner as follows:

(i) having protruding tuning probe placed closest to the test port (see ref. 9), as shown inFIG. 3,

(ii) being mounted at an angle matching the slope of the coaxial connector of the wafer probe and connected directly to it as shown inFIG. 8, and, in addition to prior art,

(iii) including a secure integrated planarity controlling probe-holding bracket extension as inFIGS. 8-12 and 16B.

BRIEF SUMMARY OF THE INVENTION

The invention consists in a new low-profile tuner design integrating a wafer-probe bracket extension with planarity control, that can hold the wafer probe securely, with the impedance tuner mounted on a 3-axis tuner positioner under an angle matching the angle of the axis of the coaxial connector of the wafer probe. The low-profile tuner has its tuning probe operating as close as physically possible to the RF adapter of the tuner test port which is directly connected to the wafer-probe coaxial connector. The new apparatus is not an obvious combination of existing work, because it offers (a) the benefit of increasing, to the maximum possible, the tuning range, (b) the benefit of allowing simultaneous planarity (THETA) control (no prior art allows the combined (a) and (b) configuration, because of the required RF cable), and (c) eliminating the need for the extension RF cable between the instrument (tuner) and the wafer-probe, including the set of two coaxial adapters of the said cable.

The integration of the bracket extension with the tuner slabline is not obvious matter either, because there is no RF cable present, able to absorb the twisting and tilting of the wafer-probe body116caused by the planarity adjustment, since the rotation axis115of the probe body is different than the rotation axis114of the coaxial connector of the probe, shown inFIG. 11. This incompatibility is absorbed by the twisting, bending and tilting capacity of the flexible septum116and the mounting technique employed which uses adjustable positioning of the septum116inside the vertical slot127and tightening with screw125. The slot traverses the horizontal segment of the horizontal segment of the L-shaped bracket extension126in which the flexible septum is inserted and is allowed to twist and tilt to absorb even small differences between bracket and probe angles.

