inp hbt 300ghz oscillator

8/17/2019 InP HBT 300GHz Oscillator

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InP HBT Voltage Controlled Oscillator for

300-GHz-Band Wireless Communications

Jae-Young Kim, Ho-Jin Song, Katsuhiro Ajito, Makoto Yaita, and Naoya Kukutsu NTT Microsystem Integration Laboratories

NTT Corporation

3-1 Morinosato-Wakamiya, Atsugi, Kanagawa, Japan [email protected]

Abstract — We present a 300-GHz-band fundamental

voltage controlled oscillator (VCO) for wireless

communications using 0.25-m InP HBT technology. The

VCO exhibits about -2-dBm differential output power and

10-GHz frequency tuning range with dc power

consumption of 46.2 mW. The oscillation frequency bandof the VCO can be extended over 360 GHz in the same

structure.

Keywords-THz wireless communication, 300 GHz, InP HBT

MMIC, voltage controlled oscillator

I. I NTRODUCTION

The progressively increasing multimedia consumption inthe mobile environment has led the development of highercapacity wireless systems with a high-order modulationscheme or wide radio bandwidth [1]. In general, the availableradio bandwidth tends to be proportional to the RF carrier

frequency. Thus, the recent emergence of millimeter-wave(mm-wave) wireless technologies using 60-GHz or 120-GHz

bands reflects the huge need for the high-speed wirelesssystems with higher carrier frequency [2-3]. In a similarmanner, the THz frequency band, especially 300 GHz, hasreceived much attention for the next generation of wirelesscommunications with over 10-Gbit/s data transmission capacity[4].

However, in the high-frequency band over 100 GHz,achieving the basic functions for communications, such as RFcarrier generation and amplification, has been challenging dueto the bandwidth limitation of electrical devices. For thisreason, the feasibility of wireless communications over 100

GHz has been demonstrated with photonic-RF generationtechniques [5-8]. As the most successful case to date, NTT hasdeveloped 120-GHz wireless communication system using a

photodiode-based photonic emitter and an integrated HEMTamplifier [5]. Later, the photonic-RF generation parts werereplaced with a monolithically integrated circuit (IC) to reducetransceiver size. [3]. The 300-GHz band wireless technology isin the early stage of development and uses photonic technologyfor THz signal generation and electrical technology for thedetector [6-7]. With this approach, the feasibility of a 300-GHzwireless link has been demonstrated with 12.5-Gbit/s datatransmission over a distance of 0.5 m [7]. The data rate and

coverage of the 300-GHz band wireless link is mainly limited by the available transmission power from the photonic emitterand the sensitivity of the detector.

Recent progress in the semiconductor processes has startedsupporting high-speed electronic devices, such as InP-based

high electron mobility transistors (HEMTs) [8] andheterojunction bipolar transistors (HBTs) [9] operating up tothe 1-THz region. In addition, the basic functional blocks, suchas a mixer [10], amplifier [11] and oscillators [12-14], have

been demonstrated at around 300-GHz band. The InP-basedintegrated circuit (IC) approach is promising for high-powersignal generation and a compact transceiver. Meanwhile,oscillators over 300-GHz band have been demonstrated basedon CMOS technology [15-16] or a resonant tunneling diode[17]. However, the output powers are not sufficient for

practical wireless transceivers.

In this paper, we present a 300-GHz band fundamentalvoltage controlled oscillator (VCO) using InP HBT technology.

The differential VCO is based on the common-collectorColpitts structure integrated with common-base output buffersin a cascade structure for operation up to 365 GHz.

II. DESIGN PRINCIPLE

The VCO was designed with the 0.25-m doubleheterojunction bipolar transistor (DHBT) process [9]. Theextrapolated maximum current gain cutoff frequency ( f t ) andmaximum power gain cutoff ( f max) of the transistor are 370 and650 GHz, separately, at a bias condition of VCE= 1.8 V and JE=8mA/m

2. The HBTs are fabricated with epitaxial layers grown

by molecular beam epitaxy on semi-insulting InP substrate. A30-nm carbon-doped base layer and chirped super-lattice

grading (InGaAs/InAlAs) are formed over the N--collector with150-nm thickness. After the HBT fabrication, the devices are

passivated with a low-k spin-on-dielectric benzocyclobutene(BCB). The back-end process includes thin-film resistors,metal-insulator-metal (MIM) capacitors, and four-layers ofinterconnects (M1-M4). The interconnect layers are formedusing a gold-based electroplating process and interlayer BCBdielectrics with 2-m thickness. The thickness of the topmostmetal (M4) is 3 m.

Fig. 1 shows a schematic of the designed VCO. The basictopology follows that of a common-collector Colpitts oscillator

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integrated with the output buffer in a cascode structure. Thedifferential operation enables virtual grounds along the centerof the symmetric structure, which greatly reduces thecomplexity of bias circuitry. Additional advantages of thedifferential VCO are common-mode noise rejection anddifferential oscillation output for the conventional Gilbert-cellmixer. The oscillator core is composed of a pair of HBTs (M

A)

commonly biased at the base. The core HBTs are 0.254 m2

in size with the bias current density for each device of 7mA/m

2. For power gain in output port and isolation of the

oscillation core, common-base output buffers (MB) were added.The cascade configuration offers advantages of bias currentreuse and simplicity in layout. In a common-collector Colpittsoscillator, the low-impedance collector of the core HBT tendsto increase the loop gain. Therefore, to obtain a low-impedanceemitter sharing the same bias current with the core HBTs, the

HBTs for the buffer (MB) are sized as 0.25 6 m2 with the

bias current density of 4.2 mA/m2 . The T-shaped buffer

matching circuits adjust the input impedance of the buffer stage

connecting the buffer to the core HBTs in the layout.

In this bias condition, collector-base capacitance C CB and base-emitter capacitance C BE of the core HBTs are estimated to be about 5 and 12 fF, respectively, from the s-parameters of theHBT. As shown in the inset of Fig. 1, a Colpitts oscillator is anLC oscillator where the feedback is taken from a capacitivevoltage divider. The ratio of feedback capacitors is animportant factor for the loop gain and is usually set from 1 to 2.Although the frequency tuning of a conventional Colpitts VCOis achieved with inductance control in the base of the core HBT,in this design, one of the feedback capacitors is employed for

the frequency tuning part. This configuration enables a simplelayout and reduces the quality factor Q degradation of theoscillator core from the lossy varactor. The frequency tuning

part is composed of a diode-connected double-finger HBT

(0.253 m2) in reverse bias and interconnections. The

equivalent capacitance of the tuning part ranges from 10 to 18fF with Q of about 15 at 300 GHz, where the ratio of feedback

capacitances is around one to one. Then, by loading inductance(25 pH) in the oscillator core, the oscillation frequency is set ataround 300 GHz by LC resonance.

The interconnections were realized with the invertedmicrostrip line (Inv-MSL) by using the topmost layer (M4) asthe ground and first interconnection metal (M1) as a signal lineto avoid parasitic inductance and power loss. The typical widthof the Inv-MSL is 4 m, of which loss is about 6.2 dB/mm andthe characteristic impedance is about 60 ohm. Although thenarrow width of the Inv-MSL introduces power loss, theadvantages of the short connection length and elimination of

GND

VO+

V1

VEE (-3.3V)

50O

Term.

(0.25?4 µm2)

MB

Tuning

part

Buffer

matching

VTUNE

VO-

MA

IEE = 14 mA

(0.25?6 µm2)

LMA

CBE

CTUNE

CCB

Fig. 1. Simplified schematic diagram of the VCO. Output signal is signal-

ended with internal termination of one output to 50 ohm.

PDiss = 3.3V x 14mA = 46.2mW

DC Bias

R

F

Harmonic

Mixer

LO source

( ~13GHz)

x24

RF-SAConversion loss:

~35dB @300GHz (estimated)

(a)

(b)

Fig. 2. (a) Chip photograph of the VCO (730690 um2) and experimental

setup for VCO measurement. (b) Harmonically down-converted oscillationoutput measured with an RF spectrum analyzer (RF-SA). Conversion loss of

the measurement setup is estimated as 35dB at 300 GHz.

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via structure are significant. One of the differential outputs wasconnected to the RF probe PAD for the on-wafer measurementusing an Inv-MSL to MSL transition while the differentialoutput was internally terminated to the 50 ohm resistor.

III. MEASUREMENT RESULTS

Fig. 2(a) shows a photograph of the fabricated chip and a

schematic diagram of the measurement setup. The on-wafermeasurement was performed with a Cascade WR-3 waveguide

probe and a VNA extender as the harmonic mixer. Bysupplying the LO signal around 13 GHz to the 24

th harmonic

mixer, the output signal around 300 GHz is down-converted tothe low-frequency band and measured with an RF spectrumanalyzer (RF-SA). The spectrum in Fig. 2(b) shows thefrequency down-converted VCO output signal. The power lossand conversion loss of the measurement setup was not

precisely calibrated and the estimated total measurement loss based on the specification of the devices is about 35 dB.

The fabricated VCO chip consumes 46.2 mW with VEE= -3.3 V as designed. The oscillation frequency of the VCO varies

by controlling the tuning voltage (VTUNE) as shown in Fig. 3(a).VTUNE varies from VEE +0.5V to VEE +2.0V, which correspondsto reverse bias voltage across the diode-connected HBT of 0 to1.5 V. The measured oscillation frequency is around 310 GHzwith the frequency tuning range of about 10 GHz.

Five variations of the VCO were designed for differentoscillation center frequencies around the 300-GHz band. TheseVCOs have an almost identical structure except for the shapeof the T-type buffer matching circuit. Fig. 3(b) shows themeasured output powers of the VCOs as a function of theoscillation frequency. The VCO with the highest frequency canoscillate up to 365 GHz. The measured single-ended output

power from the VCO is about -5 dBm at 310 GHz, whichagrees well with the simulated output power of -3 dBm,excluding the loss of Inv-MSL to MSL transition. Themeasured output power linearly decreases with frequency.However, because the power loss of our measurement setupincreases in the high-frequency region and the powercalibration data is not supported especially at over 320 GHz,

we expect the actual output powers of the VCOs are, at least,higher than the current measurement results.

IV. CONCLUSION

The 300-GHz-band fundamental VCOs have beendemonstrated using the 0.25-m InP HBT process for

broadband wireless communications system. The VCOs exhibitabout -5-dBm output power and a 10-GHz frequency tuningrange in the 300-GHz band, consuming 46.2 mW. Theoscillation frequency of the VCO can be extended up to the360-GHz region with the same circuit structure. The VCO can

be widely utilized for the 300-GHz-band integrated wirelesstransceivers.

R EFERENCES

[1] J. Wells, “Faster than fiber: The future of multi-G/s wireless,” IEEEMicrow. Mag., vol. 10, no. 3, pp. 104–112, May 2009.

[2] C. H. Doan, S. Emami, D. A. Sobel, A. M. Niknejad, and R. W.Brodersen, “Design Considerations for 60 GHz CMOS Radios,” IEEEComm. Mag., vol. 42, no. 12, pp. 132–140, Dec. 2004.

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[6] T. Nagatsuma, H. J. Song, Y. Fujimoto, K. Miyake, A. Hirata, K. Ajito,A. Wakatsuki, T. Furuta, N. Kukutsu, and Y. Kado, “Giga-bit wirelesslink using 300–400 GHz bands,” Proc. IEEE Int. Topical MeetingMicrow. Photon. (MWP), Oct. 2009, pp. 14–16.

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*excluding 35-dB

estimated power loss

(a)

(b)

310 320 330 340 350 360 370-20

-15

-10

-5

0

O u t p u t p o w e r ( d B m )

Oscillation frequency (GHz)

0.5 1.0 1.5 2.0300

305

310

315

320

325

Measurement Simulation

O s c i l l a t i o n f r e q u e n c y ( G H z )

VTUNE

-VEE

(V)

Fig. 3. (a) Measured and simulated oscillation frequencies as a function of

VCO tuning voltage and (b) measured oscillation output powers of VCOs at

different oscillation frequencies.

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[8] R. Lai, X. B. Mei, W. R. Deal, W. Yoshida, Y. M. Kim, P. H. Liu, J.Lee, J. Uyeda, V. Radisic, M. Lange, T. Gaier, L. Samoska, A. Fung,“Sub 50 nm InP HEMT Device with Fmax Greater than 1 THz,” Proc.Int. Electron Devices Meeting (IEDM), Dec. 2007, pp. 10–12.

[9] M. Urteaga, M. Seo, J. Hacker, Z. Griffith, A. Young, R. Pierson, P.Rowell, A. Skalare, and M. J. W. Rodwell, “InP HBT integrated circuittechnology for terahertz frequencies,” Proc. IEEE Compound Semicond.Integr. Circuit Symp. (CSICS), Oct. 2010, pp. 1–4.

[10] I. Kallfass, H.Massler, A. Leuther, A. Tessmann, and M. Schlechtweg,

“A 210 GHz dual-gate FET mixer MMIC with >2 dB conversion gain,high LO-to-RF isolation, and low LO-drive requirements,” IEEEMicrow. Wireless Compon. Lett., vol. 18, no. 8, pp. 557–559, Aug. 2008.

[11] V. Radisic, W. R. Deal, K. M. K. H. Leong, X. Mei, W. Yoshida, P. H.Liu, J. Uyeda, A. Fung, L. Samoska, and T. Gaier, “A 10-mWSubmillimeter-Wave Solid-State Power-Amplifier Module,” IEEETrans. Microw. Theory Tech., vol. 58, no. 7, pp. 1903–1909, Dec. 2010.

[12] V. Radisic, X. Mei, W. Deal, W. Yoshida, P. Liu, J. Uyeda, M. Barsky,L. Samoska, A. Fung, T. Gaier, and R. Lai, “Demonstration of sub-millimeter wave fundamental oscillators using 35-nm InP HEMT

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[13] M. Seo, M. Urteaga, A. Young, V. Jain, Z. Griffith, J. Hacker, P.Rowell, R. Pierson, and M. Rodwell, “>300 GHz fixed-frequency andvoltage-controlled fundamental oscillators in an InP DHBT process,”IEEE MTT-S Int. Microw. Symp. Dig., May 2010, pp. 272–275.

[14] M. Seo, M. Urteaga, M. Rodwell, and M. Choe, “A 300 GHz PLL in anInP HBT technology,” IEEE MTT-S Int. Microw. Symp. Dig., Jun.2011, pp. 1–4.

[15] B. Razavi, “A 300-GHz fundamental oscillator in 65-nm CMOStechnology,” IEEE J. Solid-State Circuits, vol. 46, no. 4, pp. 894–903,Apr. 2011.

[16] E. Seok, C. Cao, D. Shim, D. Arenas, D. Tanner, C. Hung, and K. O.Kenneth, “A 410 GHz CMOS push-push oscillator with an on-chip patch antenna,” Proc. Int. Solid-State Circuits Conf. (ISSCC), Feb. 2008, pp. 472–473.

[17] M. Asada, S. Suzuki, and N. Kishimoto, “Resonant tunneling diodes forsub-terahertz and terahertz oscillators,” Jpn. J. Appl. Phys., vol. 47, no. 6, pp. 4375–4384, Jun. 2008.

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inp hbt 300ghz oscillator

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