A Ultra High Ruggedness Performance for Multi-Mode / Multi

Shu-Hsiao Tsai, Rei-Bin Chiou, Tung

No.69, Technology 7th Rd., Hwaya Technology Park, KueiE-mail: andytsai@winfoundry.com, Phone: +886

Keywords: Multi-mode Multi-band (MMMB), Abstract InGaP/GaAs HBT has been widely used in power amplifier (PA) design for wireless communicationits high linearity and high efficiency. Multi-Mode / Multi-Band (MMMB) power amplifier plays more important role with the strong growth of smart phone. A MMMB power amplifier requires applying for GSM, UMTS and LTE applications. One of the requirements for GSM PA is the ruggedness of HBT which can maintain the same performance after the stress of high voltage standing wave ratio (VSWR) mismatch. In this paper, we present an ultra high ruggedness HBT technology which can pass the ruggedness test under VCE is 5V and VSWR 50:1. INTRODUCTION

The growth of mobile internet and multimediahas been explosive in recent years [1]. Multimode multiband (MMMB) power amplifiers have been developed in recent years for next generation mobile handsets and tablets applications. These mobile devices are required to higher data rates promised by 3G WCDMA/HSPA, and even 4G LTE standards with backward compatibility to the legacy 2G GSM and 2.5G GPRS/EDGE standards. In the meantime, a combination of frequency bands will need to be supported while reducing cost and die size of mobile devices [2].Therefore, the requirement of ruggedness, efficiency, and linearity will be needed simultaneously in HBTs for MMMB PA design.

This paper will demonstrate a InGaP/GaAs HBT with excellent ruggedness performance, qualified plinearity performance, and flexible device layout design for applying into MMMB PA design and development. DEVICE FABRICATION AND FEATURES

The ultra high ruggedness performance InGaP/GaAs HBTs were fabricated with WiN’s optimized epilayout and latest HBT process. The collector was designed to achieve not only high off-state breakdown voltage but also on-state breakdown voltage for wide safe operation area

Ultra High Ruggedness Performance of InGaP/GaAs HBT Mode / Multi-Band Power Amplifier Application

Bin Chiou, Tung-Yao Chou, Cheng-Kuo Lin, and

WiN Semiconductors Corp.

No.69, Technology 7th Rd., Hwaya Technology Park, Kuei-Shan Hsiang, Taoyuan, Taiwan 333andytsai@winfoundry.com, Phone: +886-3-3975999#151

(MMMB), Ruggedness

InGaP/GaAs HBT has been widely used in power amplifier (PA) design for wireless communications due to its high linearity and high efficiency. In recent years

Band (MMMB) power amplifier plays more important role with the strong growth of smart phone. A MMMB power amplifier requires applying for GSM, UMTS and LTE applications. One of the requirements for GSM PA is the ruggedness of HBT

me performance after the stress of high voltage standing wave ratio (VSWR) mismatch. In this paper, we present an ultra high ruggedness HBT technology which can pass the

VSWR 50:1.

internet and multimedia services Multimode multiband

(MMMB) power amplifiers have been developed in recent years for next generation mobile handsets and tablets

hese mobile devices are required to support promised by 3G WCDMA/HSPA, and even

with backward compatibility to the legacy GPRS/EDGE standards. In the meantime,

frequency bands will need to be supported size of mobile devices [2].

Therefore, the requirement of ruggedness, efficiency, and needed simultaneously in HBTs for MMMB

demonstrate a InGaP/GaAs HBT with excellent ruggedness performance, qualified power and linearity performance, and flexible device layout design for

development.

The ultra high ruggedness performance InGaP/GaAs HBTs were fabricated with WiN’s optimized epi-structure,

process. The collector was designed breakdown voltage but wide safe operation area

(SOA) [3]. The devices were fabricated latest HBT process which metal layers (M1 and M2) dielectric layer between M1 and M2. instead of using Polyimide as dielectric film better mechanical and moisture protection. The thickness otwo metal interconnection layers are 1um evaporated and 4um plated Au for M1 and M2 respectively.with unit capacitance of capacitors with unit capacitance of film resistors with sheet resistanfor MMIC designs. Fig. 1 shows cross-section.

Fig. 1 The Cross section photos of HBT unit cell

Table 1The illustration of horizontal and vertical orientation HBTs

Horizontal orientation HBTs

InGaP/GaAs HBT Band Power Amplifier Application

and Dennis Williams

Shan Hsiang, Taoyuan, Taiwan 333 3975999#1512

. The devices were fabricated by using WiN’s latest HBT process which included two interconnection

and a thicker SiN layer as the dielectric layer between M1 and M2. A thicker SiN film nstead of using Polyimide as dielectric film can provide

better mechanical and moisture protection. The thickness of two metal interconnection layers are 1um evaporated and 4

for M1 and M2 respectively. MIM capacitors with unit capacitance of 570 pF/mm2, stacked MIM capacitors with unit capacitance of 870 pF/mm2, and thin film resistors with sheet resistance of 50 Ohm/sq can be used for MMIC designs. Fig. 1 shows the SEM photo of HBT

Cross section photos of HBT unit cell.

Table 1 The illustration of horizontal and vertical orientation HBTs

Horizontal orientation HBTs Vertical orientation HBTs

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In order to achieve the application of MMMB PA, more flexible HBT design is supported in this work. Table 1 shows that two kinds of HBT unit transistor in both horizontal and vertical orientations of emitter fingers are presented in this work. As Fig. 2 shown, two orientations HBTs can be implemented into a multirealizing two power stages of high band and low band in a single die more easily and die size efficiently.

Fig. 2 The illustration of both horizontal and vertical orientation HBTs

applying to Multi-Band PA

Besides two orientations of emitter finger, this work

demonstrated two configurations of HBT unit transistor. As Table 2 shown, Type-A HBTs was the conventional layout which base metal finger surrounded emitter mesa to formB-E-B-E-B structures. In order to improve the power gain of unit HBT transistors, Type-B HBTs Compare to conventional Type-A HBTs, Typewhich was E-B-E structure removed the outer base metal fingers to reduce the base-collector capacitance (Cbc) by shrinking the base mesa area and further enhance the power gain.

Table 2 The illustration of Type-A and Type

Type-A HBTs Type

DEVICE DC & RF PERFORMANCE

The key device parameters are shown in Table 2.

shows the safe operation area of a single unit cell which theemitter size is 3um*40um*3fingers. operation area (SOA) can be achieved in this work due to

In order to achieve the application of MMMB PA, more flexible HBT design is supported in this work. Table 1

that two kinds of HBT unit transistor in both horizontal and vertical orientations of emitter fingers are

this work. As Fig. 2 shown, two orientations HBTs can be implemented into a multi-band PA for realizing two power stages of high band and low band in a single die more easily and die size efficiently.

vertical orientation HBTs

Band PA.

Besides two orientations of emitter finger, this work demonstrated two configurations of HBT unit transistor. As

A HBTs was the conventional layout emitter mesa to form the

improve the power gain of B HBTs were proposed.

A HBTs, Type-B HBTs removed the outer base metal

collector capacitance (Cbc) by mesa area and further enhance the power

A and Type-B HBTs

Type-B HBTs

The key device parameters are shown in Table 2. Fig. 3 single unit cell which the

The wider safe can be achieved in this work due to

proper collector layer design

Table 2Key device DC and RF characteristics

Parameters Current Gain @ 1.25kA/cm2

Turn-on voltage @ 1.25kA/cmBVceo @ 0.05kA/cm2 BVcbo @ 0.05kA/cm2 BVebo @ 0.05kA/cm2 Ft @ 25kA/cm2

Fig. 3 The comparison results of safe operation area (SOA) between high

ruggedness version and conventional version of collector layer design.

Fig. 4 shows the comparison

available gain (MAG) between TypeType-B HBTs show higher MAG than Typethe lower Cbc capacitance. Therefore, Typeprovide better power performance under the frequency below 3GHz for handset application

Fig. 4 The comparison results of Maximum Available Gain (MAG) between

Type-A and Type-B HBTs. Type-B HBTs show higher MAG than Type

HBTs for handset application

0 50.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7Device size: 3um x 40um x 3 fingersAmbient Temp.: 25C

Device Aas reference

Ic(m

A)

10

5

10

15

20

25

30

35

40

MA

G (

dB

)

freq. (GHz)

proper collector layer design.

Table 2 Key device DC and RF characteristics

Unit Typical Value 2 N/A 75

on voltage @ 1.25kA/cm2 V 1.265 V 18.5 V 37 V 7.0 GHz 28

safe operation area (SOA) between high

ruggedness version and conventional version of collector layer design.

comparison results of maximum ain (MAG) between Type-A and Type-B HBTs.

higher MAG than Type-A HBTs due to the lower Cbc capacitance. Therefore, Type-B HBTs can provide better power performance under the frequency

pplication.

Maximum Available Gain (MAG) between

B HBTs show higher MAG than Type-A

HBTs for handset application.

10 15 20

Device size: 3um x 40um x 3 fingersAmbient Temp.: 25C

Device Bthis work

VCE(V)

10

*Device size : 2um X 20um X 2f

freq. (GHz)

Type-A HBT

Type-B HBT

CS MANTECH Conference, April 23rd - 26th, 2012, Boston, Massachusetts, USA

As the Fig. 5 shown, Gummel plot and I-V curves of both vertical and horizontal orientations HBTs show identical result.

Fig. 5 The comparison results of Gummel Plot measurement between

horizontal and vertical orientation HBTs. The DC characteristics between

horizontal and vertical orientation HBTs are identical.

DEVICE POWER AND RUGGEDNESS PERFORMANCE Table 3 shows the results of the ruggedness test for single unit cell which the emitter size is 3um*40um*3fingers. The VSWR was fixed at 10:1 for 360 degree all phase rotation. VCE was increased from 3.6V and stop until device failed. Device-A was the reference device with the conventional collector design and the proper collector design in this work was implemented in Device-B. Device-A can only pass the ruggedness test under VCE was 5V. However Device-B started to fail until VCE went to 7.5V. According to the SOA measurement and ruggedness test results, Device-B showed not only wider SOA but also more robust ruggedness performance. The detailed test results of Device-B were shown in Fig.6.

Table 3 Ruggedness test results under VSWR 10:1 for Device-A and Device-B.

Device size is 3um*40um*3fingers.

VCE 3.6V 5V 6V 6.5V 7V 7.5V Device A Passed Passed Failed Device B Passed Passed Passed Passed Passed Failed

As Fig.7 shown, the same test vehicle of SOA

measurement and ruggedness test which the emitter size is 3um*40um*3fingers is chosen for the load-pull measurement under 900MHz. DUT was attached on an evaluation board the power performance was measured on a Focus load pull system. The device was biased at VCE was 3.6V and collector quiescent current was 10mA. The result shows there is no significant difference of power performance between Device-A and Device-B. Linear power gain is around 22.5 dB, P1dB is around 20dBm and the power added efficiency (PAE) under P1dB is around 57% for both Device-A and Device-B.

Fig. 6. The variation of DC collector current during all phase rotation for Device-B at 10:1 VSWR and 3 ~7.5V.

-16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 80

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

Pou

t (dB

m),

Gai

n (d

B)

Pin (dBm)

Device-A Device-B

PA

E(%

)

Fig. 7. Power performance comparison between Device-A and Device-B. In order to further confirm the ruggedness performance of Device-B. The ruggedness test of 8064um2 power cell which was formed by Device-B is shown as Table 4. DUT power cell was partially matched on an evaluation board and it can deliver 35dBm output power at 900 MHz. VSWR varied from 10:1 to 50:1 all phase rotation during ruggedness test at VCE was 3.6V and 5V respectively. This work shows the excellent ruggedness performance which can pass under VSWR 50:1 for both VCE was 3.6V and 5V.

Table 4 Various VSWR from 10:1 to 50:1 ruggedness test results under 35dBm output power for VCE was 3.6V and 5V. Power cell size is 8064um2.

VSWR 10:1 20:1 30:1 40:1 50:1 VCE=3.6V Passed Passed Passed Passed Passed VCE=5V Passed Passed Passed Passed Passed

-50 0 50 100 150 200 250 300 350 400

0

20

40

60

80

100

120

140

160

Frequency: 900MHzConstant Pout: 21.5dBm

Icq

(mA

)

Phase (degree)

VCE= 3.6 V VCE= 5 V VCE= 6 V VCE= 6.5 V VCE= 7 V VCE= 7.5 V

0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

0 1 2 3 4 5 60

4

8

12

16

20

Horizontal orientation HBT

Vertical orientation HBT

I C(m

A)

25

C

VCE

(V)

I C &

IB (

A)

@ 2

5C

VBE

(V)

Horizontal orientation HBT

Vertical orientation HBT

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CONCLUSIONS In conclusion, we have demonstrated an InGaP/GaAs

HBT with excellent ruggedness performance and without sacrificing its power performance. HBTs survived the ruggedness test of 50:1 VSWR at 5V VCE under 35dBm output power delivered. This device is excellent candidate for GSM applications and it can be further implemented to the MMMB PA as well, due to its flexible device designs and qualified power performance. ACKNOWLEDGEMENTS

The authors would like to thank the people that supported the measurements and wafer processing of WiN’s device characterization team and manufacturing team respectively. REFERENCES [1] N. Q. Bolton, “Mobile Device RF Front-End TAM Analysis

and Forecast,” CS Mantech Conf., May 16-19, 2011. [2] N. Cheng, “Challenges and Requirements of Multimode

Multiband Power Amplifiers for Mobile Applications,” IEEE CSICS Conf., 2011.

[3] S. Lee, “The Study of Heterojunction Bipolar Transistors for High Ruggedness Performance,” CS Mantech Conf., May 16-19, 2011.

ACRONYMS

HBT: Heterojunction Bipolar Transistor MMMB: Multimode Multiband SOA: Safe Operation Area VSWR: Voltage Standing Wave Ratio

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