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Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements J.D. Gallego, C. Diez González, I. López, I. Malo IT-CDT 2016-18 Observatorio de Yebes Apdo. 148 19080 Guadalajara SPAIN Phone: +34 949 29 03 11 Fax: +34 949 29 00 63 YebeS Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements Change Record Revision Date Affected Paragraphs(s) A 2016-11-02 All Rev. A Reason/Initiation/Remarks First Issue IT-CDT 2016-18 Page 2 of 22 YebeS Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements TABLE OF CONTENTS 1. 2. 3. 4. 5. 6. 7. Introduction ......................................................................................................................... 4 Measurement equipment ..................................................................................................... 4 Calibration ........................................................................................................................... 4 Measurements ...................................................................................................................... 5 Conclusions ......................................................................................................................... 6 Appendix I ........................................................................................................................... 9 Appendix II........................................................................................................................ 10 Rev. A IT-CDT 2016-18 Page 3 of 22 YebeS Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements 1. Introduction This report presents the results of the measurement of several types of HEMTs including the effect of bonding wires. The objective was to asset the accuracy of the models used for the design of cryogenic amplifiers. The measurements were carried out in a Probe Station in the 0.250-110 GHz frequency range at ambient temperature using the new equipment available in Yebes. The most interesting finding of this work is the resonances which appear at high frequencies (typically >50 GHz) and that were not predicted by the simple models based on equivalent circuits obtained by fitting on-wafer measurements of S parameters of the transistors plus ideal inductors to simulate bonding wires to the chip. These resonances can be explained by the parasitic capacitance of the source metallization and bonding pads of the transistors which is not usually included in the equivalent circuit. This effect appears at high frequency and does not affect much to the S parameters below 20 GHz, but can be dramatic at higher frequency, since it can produce oscillations, making the transistors virtually unusable in some cases. 2. Equipment Probe station mod. MPS 150 (Cascade Microtech) Coplanar probes mod. ACP 110-A-GSG-125 (Cascade Microtech) Vector network analyzer mod. PNA-X 5247 (Keysight) Millimeter wave controller mod. N5261A (Keysight) Millimeter wave heads mod. N5250CX10 (Keysight) Power supply mod. N3280A (Agilent) Transitions from coplanar to microstrip mod. ProbePoint 0503 (Jmicro) Coplanar calibration substrate (ISS) mod. 104-783A (Cascade Microtech) Microstrip calibration substrate mod. CM05LX (Jmicro) 3. Calibration The chip measurements were taken with a standard LRRM calibration with the Cascade Microtech calibration substrate (Impedance Standard Substrate, figure 3) using WinCal software. With the standards used this calibration performs reasonably well in all the 250MHz-110 GHz range used. It was verified with an open (probes in air) and with a long matched coplanar line (~27ps) in the ISS substrate. The ISS was used in combination with an absorbing ISS holder (SN 116-334) as recommended by Cascade. A microstrip calibration with the Jmicro calibration substrate (figure 2) and the multiline TRL (NIST type) algorithm implemented in WinCal was attempted, but it was not possible to calibrate over 90 GHz due to the limitation of the minimum line length in the Jmicro substrate. However, the microstrip lines over 5 mil alumina still perform reasonably well up to 110 GHz, as checked with measurements of the Jmicro thru (calibrated with the Cascade ISS in the coplanar reference plane). Finally, it was decided to take the microstrip measurements with the coplanar LRRM calibration but de-embedding the effect of the two coplanar to microstrip transitions. This was performed with a built-in feature of the PNA-X which allows de-embedding circuits characterized by their S-parameter files. Appendix I contain some information of the models used to generate the files used for de-embedding. Rev. A IT-CDT 2016-18 Page 4 of 22 YebeS Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements 4. Measurements Different types of devices were tested with and without bonding wires with a bias point near the optimum expected for minimum noise at ambient temperature. The details of the results of the measurements and of the parameters of the models of the equivalent circuits are shown in Table I and Appendix II. The measurements without bonding wires were taken with the chips on the Gel-Pack box used for storage. It was attempted to measure the chips mounted in the brass plate with the coplanar to microstrip transitions in place but without bonding wires. However, that measurement was not good since there was a strong coupling of the coplanar probes and the adjacent microstrip lines (transitions) terminated in open circuit. This appeared in the S parameters as a resonance which spoiled the measurement. In the case of ETH 150 end ETH 50 devices, the chip measurements were compared with the equivalent circuit provided by ETH which includes pad parasitic elements obtained by measurement of dummy structures. The new measurements agree very well with ETH model predictions. Note that the maximum frequency used initially by ETH to fit the model parameters was 40 GHz and the new measurements are taken up to 110 GHz. Obviously a better result could be obtained by tuning some equivalent circuit parameters to fit the new data but it was preferred to leave the original values to illustrate the small difference. The chip equivalent circuit parameters are kept unaltered for the comparison with the measurements with bonding wires. Only the values of Lg, Ld and Ls are re-optimized to fit the measured data. In addition, a source pad capacitor (CpadS in figure 1) is introduced in an attempt to simulate the resonances found in the measurement. Not such an elaborated chip equivalent circuit was available for the HRL 150 or the IAF 150. The HRL chip could be measured on the Gel Pack and the values of the equivalent circuit parameters were obtained by fitting to the measurements in the 0.25-110 GHz range. The IAF 150 is a smaller chip with a pitch of 100 um, and could not be directly probed in the present setup (configured for 125 um pitch). The equivalent circuit parameters of the IAF 150 device were obtained by fitting to the data obtained with three bonding wires on each side. Figure 1: Equivalent circuit used for the transistors including bonding pad parasitics. Note the presence of CpadS (Source bonding pad) which was introduced to model the resonances observed in the measurements with bonding wires. Rev. A IT-CDT 2016-18 Page 5 of 22 YebeS Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements 5. Conclusions In the results presented in Appendix II is clearly visible the problem which appears due the resonance of the parasitic capacitance of the source pads with the bonding wires. Table I shows the values of the parasitic capacitance extracted from the measurements. The fitting of the models to the measured S parameters is far from perfect, especially above the resonance. Nevertheless, the qualitative behavior is more or less predicted by this simple model. Attempts to improve the fitting with more complex topologies did not succeed in obtaining a better result. The relative values of the source pad parasitic capacitance obtained (Table I) are in agreement with what one would expect from the geometry of the transistors and pads. For example, ETH 150-1 and ETH 150-2 are identical in everything but the height of the chip and the capacitance scales (inversely) in almost the same factor as the height (~2). The highest value of parasitic capacitance is obtained for the IAF 150 HEMT which is the one with the smaller chip height. Looking at the photos of the devices it seems clear that the larger area of source pads corresponds to the ETH layouts. This suggests that the performance of these devices (respect to resonance with bonding wires) could be improved by modifying the layout, reducing the source metallization area as much as possible. The HRL 150 is the device in which the resonance effect appears at higher frequency. Coincidentally it is also the device with a smaller layout. This could explain the remarkable stable performance of the HRL 150 in cryogenic amplifiers, although it is true that the low value of transconductance also helps in this. The ETH 50 is particularly problematic since it becomes clearly unstable (|S11| >1) with bonding wires for frequencies above the resonance. It will be difficult to use this device in a cryogenic amplifier unless an extremely low source inductance of the bonding wires can be obtained in the final configuration. Note that in present measurements, even with three short bonding wires on each side, the device is marginally unstable. More tests are needed to check whether an inductance low enough can be achieved to avoid this effect in a practical configuration. Rev. A IT-CDT 2016-18 Page 6 of 22 YebeS Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements TABLE I Gate Width (um) Chip Height (um) REF Vd (V) Id (mA) ETH 150-1 150 ~95 T-245 0.5 15 ETH 150-2 150 ~170 T-273 0.5 15 ETH 50 50 ~120 T-317 0.5 5 HRL 150 150 ~120 T-78 0.75 15 IAF 150 150 50 T-315 0.5 15 PAD PARASITICS Cpg1 (pF) Cpg2 (pF) Rgsub1 (Ω) Rgsub2 (Ω) Rgsub3 (Ω) Cpd1 (pF) Cpd2 (pF) Rdsub1 (Ω) Rdsub2 (Ω) Rdsub3 (Ω) 0.0162 0.0006 14.1 42K 392K 0.0176 0.0009 13.8 74K 318K 0.0162 0.0006 14.1 42K 392K 0.0176 0.0009 13.8 74K 318K 0.0146 0.0070 10.3 98K 90K 0.0155 0.0013 9.6 73K 87K - - CHIP Eq. CKT Rg (Ω) Rd (Ω) Rs (Ω) Cgs (pF) Rgs (Ω) Cds (pF) Rds (Ω) Cgd (pF) Gm (mS) Tau (ps) 1.9 1.5 1.2 0.0984 3.8 0.0397 59.1 0.0288 187.5 0.064 1.9 1.5 1.2 0.0984 3.8 0.0397 59.1 0.0288 187.5 0.064 0.6 4.7 4.7 0.0276 7.9 0.0155 148.2 0.0112 62.1 0 0.3 1.4 0.5 0.1075 2.9 0.0471 83.62 0.0321 129.9 0.079 0.3 1.4 0.5 0.0805 3.1 0.0467 50.41 0.0431 162.3 0 CHIP Lg (nH) Ld (nH) Ls (nH) CpadS (pF) 0.0653 0.0528 0.0013 - 0.0653 0.0528 0.0013 - 0.046 0.050 0.0006 - 0.0218 0.0250 0.0051 - - 3 BW Lg (nH) Ld (nH) Ls (nH) CpadS (pF) 0.0993 0.1215 0.0413 0.1470 0.1294 0.1614 0.0471 0.0796 0.1159 0.1012 0.0513 0.1196 0.1428 0.1258 0.0376 0.1234 0.1054 0.1151 0.0256 0.2020 1 BW Parameters of the equivalent circuit of the transistors measured Lg (nH) Ld (nH) Ls (nH) CpadS (pF) 0.1114 0.1107 0.0792 0.1524 0.1297 0.1469 0.1062 0.0700 0.1159 0.1012 0.1039 0.1078 0.1168 0.1083 0.0758 0.0929 0.1020 0.1073 0.0664 0.1601 Rev. A IT-CDT 2016-18 Page 7 of 22 YebeS Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements Figure 2: Jmicro coplanar to microstrip transition and calibration substrate. The frequency range of the NIST multiline TRL calibration is limited by the length of the shortest line to ~80-90 GHz. Figure 3: Calibration substrate used for LRRM calibration on the coplanar reference plane in the 0.250-110 GHz frequency range. Rev. A IT-CDT 2016-18 Page 8 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements 6. Appendix I Model used for de-embedding J-micro coplanar to microstrip transitions. (Half of the model is used to generate S2P files used for de-embedding) S2P SNP1 File="Thru_Jmicro_cal_ISS_cascade_2.s2p" Frequencies set f or well behav ed time domain 1 Term Term2 Num=2 Z=50 Ohm Term Term1 Num=1 Z=50 Ohm S_Param SP1 Start=(0.274314214/2) GHz Stop=109.999999814 GHz Step=0.274314214 GHz Var Eqn Jmicro thru (with problems) measured PNA-X C TLINP C1 C=Cpad pF TL2 Z=51 Ohm L=len mm K=1.001 A=att F=1 GHz TanD=0.0001 Mur=1 TanM=0 Sigma=0 S2P_Eqn S2P1 S[1,1]= S[1,2]=polar(sqrt(CALC),1*Pcor/2) S[2,1]= S[2,2]= Z[1]= Z[2]= VAR Term1 Cpad=0.004 {t} len=1.45 {t} att=0 {t} S2P_Eqn S2P2 S[1,1]= S[1,2]=polar(sqrt(CALC),1*Pcor/2) S[2,1]= S[2,2]= Z[1]= Z[2]= AMPLITUDE AND PHASE CORRECTION S(4,3) S(2,1) S(3,3) S(1,1) Term Term3 Num=3 Z=50 Ohm 2 Re f S-PARAMETERS -1.0 -0.8 -0.6 freq (137.2MHz to 110.0GHz) 0 -0.2 0.0 0.2 0.4 0.6 Term Term4 Num=4 Z=50 Ohm 0.8 1.0 100 110 freq (137.2MHz to 110.0GHz) 0.0 -10 -0.4 C C2 C=Cpad pF TLINP TL3 Z=51 Ohm L=len mm K=1.001 A=att F=1 GHz TanD=0.0001 Mur=1 TanM=0 Sigma=0 -0.5 -1.0 -30 dB(S(3,4)) dB(S(1,2)) dB(S(1,1)) dB(S(3,3)) -20 -40 -50 -1.5 -2.0 -60 -2.5 -70 -80 -3.0 0 10 20 30 40 50 60 70 80 90 100 110 freq, GHz Rev. A 0 10 20 30 40 50 60 70 80 90 freq, GHz IT-CDT 2016-18 Page 9 of 22 YebeS Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements 7. Appendix II Comparison of measurements and models of the transistors tested. Rev. A IT-CDT 2016-18 Page 10 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) ETH 150 (chip height: 95 um) -0.15 freq (1.000GHz to 110.0GHz) -0.10 -0.05 0.00 0.05 0.10 0.15 freq (1.000GHz to 110.0GHz) DDS_File_Name -10 -8 -6 -4 -2 0 2 4 6 8 10 Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) ETH_150_ISS_orig freq (1.000GHz to 110.0GHz) freq (1.000GHz to 110.0GHz) Rev. A IT-CDT 2016-18 Page 11 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements ETH 150 (chip height: 95 um) 3 BW each side m1 freq=59.00GHz Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) m1 -1.5 freq (1.000GHz to 80.00GHz) -1.0 -0.5 0.0 0.5 1.0 1.5 freq (1.000GHz to 80.00GHz) DDS_File_Name ETH_150_3BW_orig -10 -8 -6 -4 -2 0 2 4 6 8 10 freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) Rev. A m2 freq=51.00GHz Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) m2 IT-CDT 2016-18 Page 12 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements ETH 150 (chip height: 95 um) 1 BW each side Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) m1 freq=35.00GHz m1 -1.5 freq (1.000GHz to 80.00GHz) -1.0 -0.5 0.0 0.5 1.0 1.5 freq (1.000GHz to 80.00GHz) DDS_File_Name ETH_150_1BW_orig -10 -8 -6 -4 -2 0 2 4 6 8 10 Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) m2 freq=21.00GHz freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) Rev. A m2 IT-CDT 2016-18 Page 13 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) ETH 150 (chip height: 170 um) 3 BW each side m1 m1 freq=75.00GHz -1.5 freq (1.000GHz to 80.00GHz) -1.0 -0.5 0.0 0.5 1.0 1.5 freq (1.000GHz to 80.00GHz) DDS_File_Name ETH_150_h160_3BW_... -10 -8 -6 -4 -2 0 2 4 6 8 10 Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) m2 freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) Rev. A m2 freq=75.00GHz IT-CDT 2016-18 Page 14 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements m1 m1 freq=57.00GHz Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) ETH 150 (chip height: 170 um) 1 BW each side -1.5 freq (1.000GHz to 80.00GHz) -1.0 -0.5 0.0 0.5 1.0 1.5 freq (1.000GHz to 80.00GHz) DDS_File_Name -10 -8 -6 -4 -2 0 2 4 6 8 10 Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) ETH_150_h160_1BW_... m2 freq=41.00GHz freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) Rev. A m2 IT-CDT 2016-18 Page 15 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) HRL 150 (chip height: 120 um) -0.15 freq (1.000GHz to 110.0GHz) -0.10 -0.05 0.00 0.05 0.10 0.15 freq (1.000GHz to 110.0GHz) DDS_File_Name -8 -6 -4 -2 0 2 4 6 8 Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) HRL_150_ISS freq (1.000GHz to 110.0GHz) freq (1.000GHz to 110.0GHz) Rev. A IT-CDT 2016-18 Page 16 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements HRL 150 (chip height: 120 um) 3 BW each side Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) m1 m1 freq=74.00GHz -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 freq (1.000GHz to 80.00GHz) 1.0 1.2 freq (1.000GHz to 80.00GHz) DDS_File_Name HRL_150_3BW -8 -6 -4 -2 0 2 4 6 8 Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) m2 m2 freq=69.00GHz freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) Rev. A IT-CDT 2016-18 Page 17 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements HRL 150 (chip height: 120 um) 1 BW each side m1 freq=64.00GHz Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) m1 -1.5 freq (1.000GHz to 80.00GHz) -1.0 -0.5 0.0 0.5 1.0 1.5 freq (1.000GHz to 80.00GHz) DDS_File_Name HRL_150_1BW -8 -6 -4 -2 0 2 4 6 8 Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) m2 freq=71.00GHz freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) Rev. A m2 IT-CDT 2016-18 Page 18 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements ETH 50 (chip height: 120 um) 3 BW each side Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) m1 freq=47.00GHz m1 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) DDS_File_Name ETH_50_Jmicro_deemb... -4 -3 -2 -1 0 1 2 3 4 Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) m2 freq=45.00GHz freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) Rev. A m2 IT-CDT 2016-18 Page 19 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements ETH 50 (chip height: 120 um) 1 BW each side Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) m1 freq=39.00GHz m1 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) DDS_File_Name ETH_50_Jmicro_deemb... -4 -3 -2 -1 0 1 2 3 4 Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) m2 freq=27.00GHz freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) Rev. A m2 IT-CDT 2016-18 Page 20 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements IAF 150 (chip height: 50 um) 3 BW each side Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) m1 m1 freq=71.00GHz -1.5 freq (1.000GHz to 80.00GHz) -1.0 -0.5 0.0 0.5 1.0 1.5 freq (1.000GHz to 80.00GHz) DDS_File_Name IAF_150_3BW_test -8 -6 -4 -2 0 2 4 6 8 Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) m2 m2 freq=69.00GHz freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) Rev. A IT-CDT 2016-18 Page 21 of 22 Observatorio de Yebes Apartado 148, 19080 Guadalajara, SPAIN YebeS Effect of Source Bonding Wires in HEMT devices: Probe Station Measurements IAF 150 (chip height: 50 um) 1 BW each side Smodel(1,2) Smeas(1,2) Smodel(1,1) Smeas(1,1) m1 m1 freq=46.00GHz -1.5 freq (1.000GHz to 80.00GHz) -1.0 -0.5 0.0 0.5 1.0 1.5 freq (1.000GHz to 80.00GHz) DDS_File_Name -8 -6 -4 -2 0 2 4 6 8 Smeas(2,2) Smodel(2,2) Smeas(2,1) Smodel(2,1) IAF_150_1BW_test m2 m2 freq=39.00GHz freq (1.000GHz to 80.00GHz) freq (1.000GHz to 80.00GHz) Rev. A IT-CDT 2016-18 Page 22 of 22