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ESPRIT II projects on compound semiconductors
MicroelectronicEngineering15 (1991) 79-86 Elsevier
79
E S P R I T II P r o j e c t s o n C o m p o u n d S e m i c o n d u c t o r s J Mun and A Mbaye* BNR Europe Ltd, London Road, Harlow, Essex, CM17 9NA, UK *CEC, DG XIII-ESPRIT, Rue de la Loi 200, B-1049 Brussels, Belgium
Abstract The current ESPRIT II programme on Compound Semiconductors involves the effort of approximately 330 m a n years in Europe. The progrnmme is made up of six projects which embrace a wide range of devices and circuits. This paper highlights the main goal of these projects and some of their recent achievements.
1.
INTRODUCTION
There are six projects on Compound Semiconductors u n d er the current ESPRIT II programme. These projects involve approximately 330 m a n years of effort between 1989 and 1993. Projects vary from two and half years to four years in duration and apart from one project, they all started in J a n u a r y 1990. Each project has a well defined application pull. A project centred on advanced transistors for example, is pulled by the need of these transistors for high performance integrated circuits. A project centred on MMICs is pulled in its turn, by the need of these circuits for various system requirements. The projects can be examined from several angles. In this paper, we shall examine them by the frequency bands which they cover. This reflects to some extent the technology and devices being pursued by each project. Some projects are concerned with basic technologies, for example, the development of non-toxic precursors. These projects can be regarded as horizontal technology projects which would complement the more vertical projects with circuit and system pulls. The projects are summarised in table 1, including the participants to each project. Exotic acronyms can be derived from the project titles, but how some acronyms are derived remains a mystery! Broadly speaking, the ESPRIT II programme on Compound Semiconductors is pivoted on two A-type projects each with over 100 man years of effort. These 0167-9317/91/$3.50 © 1991 - Elsevier SciencePublishers B.V. All fights reserved.
80
.[. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors
Project No. (ACRONYM)
Title
Participants
5018 (COSMIC)
GaAs Monolithic Analogue Circuits for Microwave Communication Systems up to 23 GHz
Siemens (Ge), Marconi (UK), Telettra (It and Sp), Telefonica (Sp), FORTH (Gr), Jansen (Ge), ArguMens (Ge), Univ. Madrid (Sp), Univ. Rome (It), PT Torino (It)
5032 (AIMS)
Advanced Integrated Millimeter-wave Sub-assemblies
Thomson (Fr),Daimler Benz (Ge), Alcatel Espace (Fr),Univ. Lille (Fr), Electronik Centralen (De)
2035 (GIANTS)*
Advanced InGaAs-based Devices for High-speed ICs
* started in 1989
Retitled: GaInAs Novel Transistors
Marconi (UK), BNR-Europe (UK), Philips-LEP (Fr),Thomson (Fr), Picogiga (Fr),F O R T H (Gr), Farran Tech. (Ir),Univ. Lille(Fr),Univ. Madrid (Sp)
5052 (MONOFAST)
Monolithic Integration Beyond 26.5 GHz
Univ. Glasgow (UK), Alcatel Espace (Fr), GaAs Code (UK), Univ. Cambridge (UK), Farran Tech. (Ir), NMRC (Ir)
5031 (MORSE)
Metal Organic Research for Semiconductor Epitaxy
Thomson (Fr),C N E T (Fr),R S R E (UK), F O R T H (Gr), Univ. Aachen (Ge), Univ. Stuttgart (Ge), Preussag (Ge), RiDer (Fr),SMI (Fr), Univ. Padova (It)
5003 (PLANET)
Multi-wafer PLANET MOVPE Reactor
Philips - LEP (Fr),Aixtron (Ge), Polyflow (Be), Philips (Ne), Telefonica (Sp), Univ. Poly. Madrid (Sp)
Table 1: C u r r e n t ESPRIT II projects on Compound Semiconductors a n d t h e i r participants. The prime contractors are u n d e r l i n e d projects are COSMIC and AIMS. Although these projects also involve a s u b s t a n t i a l Amount of horizontal activities in the a r e a s of devices a n d technology, t h e y are n e v e r t h e l e s s very m u c h systems driven w h e r e the t a r g e t specifications a n d functionalities of the devices and circuits are defined from s y s t e m studies. B e t w e e n COSMIC and AIMS, the projects cover frequency b a n d s b e t w e e n a p p r o x i m a t e l y 1 to 20 GHz and 20 to 30 GHz respectively. These two A-type projects are complemented by two smaller B-type projects, MONOFAST a n d GIANTS. MONOFAST is concerned with technology a n d MMIC design technique focused at 44 GHz and GIANTS is concerned with the d e v e l o p m e n t of InGaAs based transistors w h e r e one of the aims is to d e m o n s t r a t e
81
J. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors a low noise amplifier MMIC at 60 GHz.
Another aim is to demonstrate
optoelectronic integration on InP substrates. The four application and device led projects are further complemented by two material orientated B-projects, MORSE and PLANET. MORSE is concerned with the development of non-toxic precursors and MOMBE growth and PLANET is concerned with the development of a multi-wafer MOVPE reactor capable of growing GaAs and InP based materials. The key areas covered by each project are summarised in table 2. I n the following sections we will try to give a brief description on each project and
a few highlights.
Systems
5018 COSMIC
5032 AIMS
navigation, mobile comm., DBS, point
short-hop link, satellite comm., ultra small sat. terminal
to multipoint, opticaltrans. ICs
LNA, RFA/mixer, Trans imp. amp.
T/R switch, LNA, SSPA,
5052 MONOFAST
LNA
2035 GIANTS
5031 MORSE
5003 PLANET
Breadhand amp.,
LNA, O/E integ.
mixer s
VCO Devices
Epitaxy
MESFET HEMT
MBE
MESFET HEMT PMI-IEMT HBT (GalnP)
MESFET
MBE MOVPE
MBE
PMHEMT HEMT (IMP) BEFET (IMP)
HEMT (GaInP) HBT
MBE MOVPE
MOMBE MOVPE
Material
HEMT laser
(GaAs) opt.wg
(IMP) MOVPE
Non-toxic precursors
Equipment
Approx. frequency coverage
MOMBE cracker cell 1 to 23 GHz
20 to 30 GHz
44 GHz
2" and3" multi-wafer reactor
1 to 60 GHz
Table 2: Key areas covered by each project. The systems are application pulls which defined the IC target specifications. 2.
P R O J E C T 5018 - "COSMIC"
This project is led by Siemens and it addresses components for applications which span between 1 to 20 GHz. Within this frequency range, attention is focused on
82
]. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors
the L, X and ka-bands. At L-band, one of the key interests is on high gain, over 60 dB, transimpedance amplifiers for high speed optical receiver applications. A sub-group in this project is investigating different circuit topologies but using essentially a well established GaAs MESFET technology. This technology is also used for RF amplifier/mixer MMICs required for mobile communication and navigation systems. At X-band, the interest is centred on components for DBS. Two approaches to MMICs are being examined, one is based on a structural array technology and another on a high packing density technology. Both approaches use MESFETs but with 0.3 ~tm/0.5 gm gate length technology with the aim of integrating several DBS receiver functions such as RFA/mixer/post amp/IF amp etc. on a single compact chip. The low noise front-end is provided by a HEMT MMIC. Preliminary results obtained from a 2-stage LNA using 0.4 ~m HEMT have exhibited 15 dB gain and 1.8 dB noise figure. The main application at ka-band is for point-to-multipoint services. The higher frequency operation at 18 to 20 GHz calls for technology improvements especially in the areas of sub-micron HEMT and self-aligned techniques. At a materials level, the advantages of laser assisted MBE growth is also being investigated. 3.
PROJECT
5032 - "AIMS"
This project is led by Thomson and it addresses components up to sub-systems level for applications between 20 and 30 GHz. System pulls are from short-hop land links and ultra-small aperture satellite terminals (USAT). A range of generic MMICs are being developed covering transmit/receive (T/R) switches, low noise amplifiers (LNAs), non-linear circuits, voltage controlled oscillators (VCOs) and solid state power amplifiers (SSPAs). Apart from the T/R switch, which makes use of the well established MESFET, all other circuits are based on the use of heterojunction transistors, ie. HEMT, pseudomorphic HEMT (PMHEMT) and HBT. Some of the FETs have been developed to a very high level of performance in readiness for application in integrated circuits. The performances achieved by 0.25 ~Lm gate length HEMT and PMHEMT are as follows:
gin fT f~ NF Gain NF Gain
@ 12 GHz @ 12 GHz @ 18 GHz @ 18 GHz
HEMT
PMHEMT
350 55 110 0.55 11.0 0.65 9.0
700 100 200 0.7 14.0 0.9 11.0
mS/ram GHz GHz dB dB dB dB
J. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors
83
The project is also investigating the novel use of several variants of the HEMT and PMHEMT for non-linear applications and for power generation. Multichannel HEMTs with planar doping are being studied to tailor the transconductance profile to realise mixer operation either in the fundamental mode or in the doubler mode. Double heterojunction PMHEMTs with planar doping are being pursued for high efficiency power transistors. 0.25 }~m gate length devices have demonstrated 120 mW output power at 1 dB compression, with 10 dB associated gain and 44% power added efficiency at 18 GHz. HBTs are also being investigated for power transistor applications but with a novel GaInP/GaAs structure rather than the conventional GaAIAs/GaAs. The larger bandgap layer is expected to give better device performance and process control. The first GaInP/GaAs microwave HBTs have already been made, exhibiting fw and fm~ of 30 GHz and 45 GHz respectively. 4.
P R O J E C T 5052 - '2VIONOFAST'
The overall aim of this project is to integrate unfamiliar technologies and new design tools into a proven methodology for high frequency MMICs. The project is led by Glasgow University and it has the participation of a number of industrial partners. The close interaction between technology and design is aimed at minimising circuit sensitivity to device variations. A sub-micron MESFET based LNA MMIC at 44 GHz is used as a vehicle to illustrate this methodology. Design starts from the FET physical parameters in terms of semiconductor material, gate length, recess depth etc. From these physical specifications the electrical properties of the device can be predicted. Using the device equivalent circuit model derived from the physical device simulator, the design then proceeds to an amplifier circuit. The sensitivity of the amplifier performance to the device parameters and then to the physical parameters can thus be analysed. This study has shown that the most critical variables are the thickness of the epilayer and the depth of the gate recess. The subsequent technology optimisation was then focused on the control of these parameters.
Another aspect of the design work involves the study of coplanar waveguides. This transmission medium is chosen for M M I C s at 44 G H z and beyond, because it eliminates problems caused by via hole inductance. At the technology level, it has been demonstrated that the MBE growth can give the required control of epilayer thickness. Work is focused on the dry etching of the gate recess. One approach is to use a selective etch by incorporating an A1GaAs etch stop layer, the other is a non-selective slow etch. Another technology area being investigated is how to reproducibly realise a 0.2 pm long T-shaped gate in order to achieve low gate resistance. In addition to conventional multi-layer ebeam lithography, the project is assessing the use of ion-beams and a combination of ion-beam with e-beam.
84 5.
]. Mun, .4. Mbco,e / ESPRIT H projects on compound semiconductors PROJECT
2035 - "GIANTS"
This project has had a head start of one year compared to the other projects, ie. January 1989 rather than January 1990. The project is led by Marconi, Caswell and the objective is to investigate novel FETs on GaAs and InP substrates which make use of an InGaAs channel layer. At the start of the project, these transistors were relatively immature and several device options were examined. However, during the course of the project the consortium has narrowed down to three devices and each device is being incorporated into integrated circuits. One particular aspect of collaboration in this project is the role played by Picogiga. They have developed various MBE layer structures based on the feedbacks of the device partners, and the device partner have in turn relied heavily on these materials for their device development work. The transistors being focused on by this consortium are the PMHEMT, the AlInAs/InGaAa/InP lattice matched HEMT on InP and the AlInAs/InGaAs/InP barrier enhanced FET also on InP. The PMHEMT has demonstrated 675 mS/mm transconductance from 0.251zm gate length devices with an fw of up to 130 GHz. This device is being used to demonstrate a broadband amplifier MMIC up to 30 GHz. The lattice matched HEMT on ImP has exhibited over 770 mS/mm transconductance from 0.25 rum gate length devices with an fw in the region of 90 GHz. This device is being used in a low noise amplifier MMIC aimed at 60 GHz. The barrier enhanced FET mokes use of a thin layer of undoped AlInAs to enhance the Schottky barrier to a doped InGaAs FET channel on InP. 1.5 pm gate length devices have exhibited over 200 mS/mm transconductance and a two stage cascode amplifier circuit has been fabricated with this device exhibiting 20 dB gain and a bandwidth over 2 GHz. This device is being used to integrate with a GaInAs photodetector diode for long wavelength optical receiver applications. 6.
PROJECT
5 0 3 1 - '~VIORSE"
There are two goals in this project led by Thomson. One goal is the development of new, less hazardous precursors and the verification of the q, lality of these precursors by MOVPE. In parallel, the second goal is concerned with the development of MOMBE growth and the realisation of equipment improvements. GaAs HBT and HEMT are used as vehicles for assessing the epilayer quality from MOVPE and MOMBE respectively. In the case of the HEMT, a novel GaInP donor layer is used instead of the more conventional GaAlAs. Good quality tertiary-butyl-phosphine (TBP) has been successfully synthesised and quaternary InGaAsP layers emitting around 1.3 pm can now be grown routinely when TBP is used with arsine. Although further purification is desirable, the present attained purity is probably already adequate for most applications. On the group III side, good progress has been made on the use of dimethylaminopropyl-dimethyl-indium (DADI). High quality InP with a 77K mobility of
J. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors
85
greater t h a n 110,000 cm2/Vshas been demonstrated. DADI has also been used in combination with TBP to grow InP and it has been demonstrated that there are no parasitic side reactions between these two precursors even at atmospheric pressure. A major objective in the MOMBE area is the growth of P and A1 based compounds with a wide range of n and p doping and a reduced residual carbon concentration. The investigation involves the systematic growth and assessment of A1GaAs using four selected A1 precursors and of GaInP using three selected precursors and a new high efficiency cracker cell. Recently, residual carbon concentration in A]GaAs has been reduced to less than 8X1017cm-a and oxygen concentration to less than 6x10 TM cm3. A new high efficiency cracker cell has been demonstrated for group V hydrides. The conventional high operating temperature of approximately 1000"C for phosphine has been a potential source of impurities. The new cell uses molybdenum as a catalyst, and preliminary results have shown a 100% phosphine cracking efficiency at 800°C. 7.
P R O J E C T 5003 - ' ~ L A N E T '
The objective of this project is to develop a high throughput multi-wafer MOVPE reactor suitable for the growth ofheterostructures required for microelectronic and optoelectronic devices. The project is led by Philips-LEP and the initial reactor chamber optimisation is based on multiple 2" wafers, leading to multiple 3" wafers. The quality of the wafers are assessed by the fabrication of GaAs HEMT and PMHEMT, GaAs based lasers and optical waveguides on InP. The MOVPE reactor being optimised under this project allows for the simultaneous growth of seven wafers in a planetary motion, using a circular growth chamber with horizontal geometry and radial gas flow. In this concept, the radial flow generates an almost linear decrease of the growth rates with increasing radius due to the depletion of the gas phase. Each wafer rotates around its own axis, and in combination with the growth rate, the growth produces a slightly concave or convex epilayer thickness profile over the wafers. The use of separate inlets of group III and group V compounds directly into the hot zone of the growth chamber allows for fine tuning of the concavity/convexity. This fine tuning is carried out with detailed modelling of the gas dynamics in the chamber. The quality of the wafers for HEMT has been evaluated by fabricating 0.5 p~mgate length devices and good performances have been obtained with an f-r of 35 GHz and a noise figure of 1.1 dB at 12 GHz. One particularly impressive aspect of these wafers is their very low surface defect density of below 10 defects cm2. The record observed to date being 0.5 defects cm -2. Pseudomorphic GaInAs layers have also been grown exhibiting Hall mobilities of 6000 cm2/Vs at 300K with 2x1012 cm "2 sheet carrier concentration. A PMHEMT with 0.5 pm gate length has exhibited an fw of 50 GHz.
86 8.
J. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors CONCLUSIONS
We have e x a m i n e d briefly the m a i n objectives of each E S P R I T II project on Compound Semiconductors and how they complement each other to m a k e up a strong overall p r o g r a m m e in the microelectronics sector. T h e r e is a large a m o u n t of results achieved by these projects, b u t with a limited space, we have choosen only some highlights for this paper. The p r o g r a m m e covers a wide range of very specialised technical areas which collectively, m a k e up the foundation of the III-V industry. It is difficult to envisage a single company alone having the resources to tackle all these areas. The synergy and the necessity of collaboration is therefore evident. 9.
REFERENCES
1990 A n n u a l Reports from projects 2035, 5003, 5013, 5018, 5035 a n d 5052.
79
E S P R I T II P r o j e c t s o n C o m p o u n d S e m i c o n d u c t o r s J Mun and A Mbaye* BNR Europe Ltd, London Road, Harlow, Essex, CM17 9NA, UK *CEC, DG XIII-ESPRIT, Rue de la Loi 200, B-1049 Brussels, Belgium
Abstract The current ESPRIT II programme on Compound Semiconductors involves the effort of approximately 330 m a n years in Europe. The progrnmme is made up of six projects which embrace a wide range of devices and circuits. This paper highlights the main goal of these projects and some of their recent achievements.
1.
INTRODUCTION
There are six projects on Compound Semiconductors u n d er the current ESPRIT II programme. These projects involve approximately 330 m a n years of effort between 1989 and 1993. Projects vary from two and half years to four years in duration and apart from one project, they all started in J a n u a r y 1990. Each project has a well defined application pull. A project centred on advanced transistors for example, is pulled by the need of these transistors for high performance integrated circuits. A project centred on MMICs is pulled in its turn, by the need of these circuits for various system requirements. The projects can be examined from several angles. In this paper, we shall examine them by the frequency bands which they cover. This reflects to some extent the technology and devices being pursued by each project. Some projects are concerned with basic technologies, for example, the development of non-toxic precursors. These projects can be regarded as horizontal technology projects which would complement the more vertical projects with circuit and system pulls. The projects are summarised in table 1, including the participants to each project. Exotic acronyms can be derived from the project titles, but how some acronyms are derived remains a mystery! Broadly speaking, the ESPRIT II programme on Compound Semiconductors is pivoted on two A-type projects each with over 100 man years of effort. These 0167-9317/91/$3.50 © 1991 - Elsevier SciencePublishers B.V. All fights reserved.
80
.[. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors
Project No. (ACRONYM)
Title
Participants
5018 (COSMIC)
GaAs Monolithic Analogue Circuits for Microwave Communication Systems up to 23 GHz
Siemens (Ge), Marconi (UK), Telettra (It and Sp), Telefonica (Sp), FORTH (Gr), Jansen (Ge), ArguMens (Ge), Univ. Madrid (Sp), Univ. Rome (It), PT Torino (It)
5032 (AIMS)
Advanced Integrated Millimeter-wave Sub-assemblies
Thomson (Fr),Daimler Benz (Ge), Alcatel Espace (Fr),Univ. Lille (Fr), Electronik Centralen (De)
2035 (GIANTS)*
Advanced InGaAs-based Devices for High-speed ICs
* started in 1989
Retitled: GaInAs Novel Transistors
Marconi (UK), BNR-Europe (UK), Philips-LEP (Fr),Thomson (Fr), Picogiga (Fr),F O R T H (Gr), Farran Tech. (Ir),Univ. Lille(Fr),Univ. Madrid (Sp)
5052 (MONOFAST)
Monolithic Integration Beyond 26.5 GHz
Univ. Glasgow (UK), Alcatel Espace (Fr), GaAs Code (UK), Univ. Cambridge (UK), Farran Tech. (Ir), NMRC (Ir)
5031 (MORSE)
Metal Organic Research for Semiconductor Epitaxy
Thomson (Fr),C N E T (Fr),R S R E (UK), F O R T H (Gr), Univ. Aachen (Ge), Univ. Stuttgart (Ge), Preussag (Ge), RiDer (Fr),SMI (Fr), Univ. Padova (It)
5003 (PLANET)
Multi-wafer PLANET MOVPE Reactor
Philips - LEP (Fr),Aixtron (Ge), Polyflow (Be), Philips (Ne), Telefonica (Sp), Univ. Poly. Madrid (Sp)
Table 1: C u r r e n t ESPRIT II projects on Compound Semiconductors a n d t h e i r participants. The prime contractors are u n d e r l i n e d projects are COSMIC and AIMS. Although these projects also involve a s u b s t a n t i a l Amount of horizontal activities in the a r e a s of devices a n d technology, t h e y are n e v e r t h e l e s s very m u c h systems driven w h e r e the t a r g e t specifications a n d functionalities of the devices and circuits are defined from s y s t e m studies. B e t w e e n COSMIC and AIMS, the projects cover frequency b a n d s b e t w e e n a p p r o x i m a t e l y 1 to 20 GHz and 20 to 30 GHz respectively. These two A-type projects are complemented by two smaller B-type projects, MONOFAST a n d GIANTS. MONOFAST is concerned with technology a n d MMIC design technique focused at 44 GHz and GIANTS is concerned with the d e v e l o p m e n t of InGaAs based transistors w h e r e one of the aims is to d e m o n s t r a t e
81
J. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors a low noise amplifier MMIC at 60 GHz.
Another aim is to demonstrate
optoelectronic integration on InP substrates. The four application and device led projects are further complemented by two material orientated B-projects, MORSE and PLANET. MORSE is concerned with the development of non-toxic precursors and MOMBE growth and PLANET is concerned with the development of a multi-wafer MOVPE reactor capable of growing GaAs and InP based materials. The key areas covered by each project are summarised in table 2. I n the following sections we will try to give a brief description on each project and
a few highlights.
Systems
5018 COSMIC
5032 AIMS
navigation, mobile comm., DBS, point
short-hop link, satellite comm., ultra small sat. terminal
to multipoint, opticaltrans. ICs
LNA, RFA/mixer, Trans imp. amp.
T/R switch, LNA, SSPA,
5052 MONOFAST
LNA
2035 GIANTS
5031 MORSE
5003 PLANET
Breadhand amp.,
LNA, O/E integ.
mixer s
VCO Devices
Epitaxy
MESFET HEMT
MBE
MESFET HEMT PMI-IEMT HBT (GalnP)
MESFET
MBE MOVPE
MBE
PMHEMT HEMT (IMP) BEFET (IMP)
HEMT (GaInP) HBT
MBE MOVPE
MOMBE MOVPE
Material
HEMT laser
(GaAs) opt.wg
(IMP) MOVPE
Non-toxic precursors
Equipment
Approx. frequency coverage
MOMBE cracker cell 1 to 23 GHz
20 to 30 GHz
44 GHz
2" and3" multi-wafer reactor
1 to 60 GHz
Table 2: Key areas covered by each project. The systems are application pulls which defined the IC target specifications. 2.
P R O J E C T 5018 - "COSMIC"
This project is led by Siemens and it addresses components for applications which span between 1 to 20 GHz. Within this frequency range, attention is focused on
82
]. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors
the L, X and ka-bands. At L-band, one of the key interests is on high gain, over 60 dB, transimpedance amplifiers for high speed optical receiver applications. A sub-group in this project is investigating different circuit topologies but using essentially a well established GaAs MESFET technology. This technology is also used for RF amplifier/mixer MMICs required for mobile communication and navigation systems. At X-band, the interest is centred on components for DBS. Two approaches to MMICs are being examined, one is based on a structural array technology and another on a high packing density technology. Both approaches use MESFETs but with 0.3 ~tm/0.5 gm gate length technology with the aim of integrating several DBS receiver functions such as RFA/mixer/post amp/IF amp etc. on a single compact chip. The low noise front-end is provided by a HEMT MMIC. Preliminary results obtained from a 2-stage LNA using 0.4 ~m HEMT have exhibited 15 dB gain and 1.8 dB noise figure. The main application at ka-band is for point-to-multipoint services. The higher frequency operation at 18 to 20 GHz calls for technology improvements especially in the areas of sub-micron HEMT and self-aligned techniques. At a materials level, the advantages of laser assisted MBE growth is also being investigated. 3.
PROJECT
5032 - "AIMS"
This project is led by Thomson and it addresses components up to sub-systems level for applications between 20 and 30 GHz. System pulls are from short-hop land links and ultra-small aperture satellite terminals (USAT). A range of generic MMICs are being developed covering transmit/receive (T/R) switches, low noise amplifiers (LNAs), non-linear circuits, voltage controlled oscillators (VCOs) and solid state power amplifiers (SSPAs). Apart from the T/R switch, which makes use of the well established MESFET, all other circuits are based on the use of heterojunction transistors, ie. HEMT, pseudomorphic HEMT (PMHEMT) and HBT. Some of the FETs have been developed to a very high level of performance in readiness for application in integrated circuits. The performances achieved by 0.25 ~Lm gate length HEMT and PMHEMT are as follows:
gin fT f~ NF Gain NF Gain
@ 12 GHz @ 12 GHz @ 18 GHz @ 18 GHz
HEMT
PMHEMT
350 55 110 0.55 11.0 0.65 9.0
700 100 200 0.7 14.0 0.9 11.0
mS/ram GHz GHz dB dB dB dB
J. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors
83
The project is also investigating the novel use of several variants of the HEMT and PMHEMT for non-linear applications and for power generation. Multichannel HEMTs with planar doping are being studied to tailor the transconductance profile to realise mixer operation either in the fundamental mode or in the doubler mode. Double heterojunction PMHEMTs with planar doping are being pursued for high efficiency power transistors. 0.25 }~m gate length devices have demonstrated 120 mW output power at 1 dB compression, with 10 dB associated gain and 44% power added efficiency at 18 GHz. HBTs are also being investigated for power transistor applications but with a novel GaInP/GaAs structure rather than the conventional GaAIAs/GaAs. The larger bandgap layer is expected to give better device performance and process control. The first GaInP/GaAs microwave HBTs have already been made, exhibiting fw and fm~ of 30 GHz and 45 GHz respectively. 4.
P R O J E C T 5052 - '2VIONOFAST'
The overall aim of this project is to integrate unfamiliar technologies and new design tools into a proven methodology for high frequency MMICs. The project is led by Glasgow University and it has the participation of a number of industrial partners. The close interaction between technology and design is aimed at minimising circuit sensitivity to device variations. A sub-micron MESFET based LNA MMIC at 44 GHz is used as a vehicle to illustrate this methodology. Design starts from the FET physical parameters in terms of semiconductor material, gate length, recess depth etc. From these physical specifications the electrical properties of the device can be predicted. Using the device equivalent circuit model derived from the physical device simulator, the design then proceeds to an amplifier circuit. The sensitivity of the amplifier performance to the device parameters and then to the physical parameters can thus be analysed. This study has shown that the most critical variables are the thickness of the epilayer and the depth of the gate recess. The subsequent technology optimisation was then focused on the control of these parameters.
Another aspect of the design work involves the study of coplanar waveguides. This transmission medium is chosen for M M I C s at 44 G H z and beyond, because it eliminates problems caused by via hole inductance. At the technology level, it has been demonstrated that the MBE growth can give the required control of epilayer thickness. Work is focused on the dry etching of the gate recess. One approach is to use a selective etch by incorporating an A1GaAs etch stop layer, the other is a non-selective slow etch. Another technology area being investigated is how to reproducibly realise a 0.2 pm long T-shaped gate in order to achieve low gate resistance. In addition to conventional multi-layer ebeam lithography, the project is assessing the use of ion-beams and a combination of ion-beam with e-beam.
84 5.
]. Mun, .4. Mbco,e / ESPRIT H projects on compound semiconductors PROJECT
2035 - "GIANTS"
This project has had a head start of one year compared to the other projects, ie. January 1989 rather than January 1990. The project is led by Marconi, Caswell and the objective is to investigate novel FETs on GaAs and InP substrates which make use of an InGaAs channel layer. At the start of the project, these transistors were relatively immature and several device options were examined. However, during the course of the project the consortium has narrowed down to three devices and each device is being incorporated into integrated circuits. One particular aspect of collaboration in this project is the role played by Picogiga. They have developed various MBE layer structures based on the feedbacks of the device partners, and the device partner have in turn relied heavily on these materials for their device development work. The transistors being focused on by this consortium are the PMHEMT, the AlInAs/InGaAa/InP lattice matched HEMT on InP and the AlInAs/InGaAs/InP barrier enhanced FET also on InP. The PMHEMT has demonstrated 675 mS/mm transconductance from 0.251zm gate length devices with an fw of up to 130 GHz. This device is being used to demonstrate a broadband amplifier MMIC up to 30 GHz. The lattice matched HEMT on ImP has exhibited over 770 mS/mm transconductance from 0.25 rum gate length devices with an fw in the region of 90 GHz. This device is being used in a low noise amplifier MMIC aimed at 60 GHz. The barrier enhanced FET mokes use of a thin layer of undoped AlInAs to enhance the Schottky barrier to a doped InGaAs FET channel on InP. 1.5 pm gate length devices have exhibited over 200 mS/mm transconductance and a two stage cascode amplifier circuit has been fabricated with this device exhibiting 20 dB gain and a bandwidth over 2 GHz. This device is being used to integrate with a GaInAs photodetector diode for long wavelength optical receiver applications. 6.
PROJECT
5 0 3 1 - '~VIORSE"
There are two goals in this project led by Thomson. One goal is the development of new, less hazardous precursors and the verification of the q, lality of these precursors by MOVPE. In parallel, the second goal is concerned with the development of MOMBE growth and the realisation of equipment improvements. GaAs HBT and HEMT are used as vehicles for assessing the epilayer quality from MOVPE and MOMBE respectively. In the case of the HEMT, a novel GaInP donor layer is used instead of the more conventional GaAlAs. Good quality tertiary-butyl-phosphine (TBP) has been successfully synthesised and quaternary InGaAsP layers emitting around 1.3 pm can now be grown routinely when TBP is used with arsine. Although further purification is desirable, the present attained purity is probably already adequate for most applications. On the group III side, good progress has been made on the use of dimethylaminopropyl-dimethyl-indium (DADI). High quality InP with a 77K mobility of
J. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors
85
greater t h a n 110,000 cm2/Vshas been demonstrated. DADI has also been used in combination with TBP to grow InP and it has been demonstrated that there are no parasitic side reactions between these two precursors even at atmospheric pressure. A major objective in the MOMBE area is the growth of P and A1 based compounds with a wide range of n and p doping and a reduced residual carbon concentration. The investigation involves the systematic growth and assessment of A1GaAs using four selected A1 precursors and of GaInP using three selected precursors and a new high efficiency cracker cell. Recently, residual carbon concentration in A]GaAs has been reduced to less than 8X1017cm-a and oxygen concentration to less than 6x10 TM cm3. A new high efficiency cracker cell has been demonstrated for group V hydrides. The conventional high operating temperature of approximately 1000"C for phosphine has been a potential source of impurities. The new cell uses molybdenum as a catalyst, and preliminary results have shown a 100% phosphine cracking efficiency at 800°C. 7.
P R O J E C T 5003 - ' ~ L A N E T '
The objective of this project is to develop a high throughput multi-wafer MOVPE reactor suitable for the growth ofheterostructures required for microelectronic and optoelectronic devices. The project is led by Philips-LEP and the initial reactor chamber optimisation is based on multiple 2" wafers, leading to multiple 3" wafers. The quality of the wafers are assessed by the fabrication of GaAs HEMT and PMHEMT, GaAs based lasers and optical waveguides on InP. The MOVPE reactor being optimised under this project allows for the simultaneous growth of seven wafers in a planetary motion, using a circular growth chamber with horizontal geometry and radial gas flow. In this concept, the radial flow generates an almost linear decrease of the growth rates with increasing radius due to the depletion of the gas phase. Each wafer rotates around its own axis, and in combination with the growth rate, the growth produces a slightly concave or convex epilayer thickness profile over the wafers. The use of separate inlets of group III and group V compounds directly into the hot zone of the growth chamber allows for fine tuning of the concavity/convexity. This fine tuning is carried out with detailed modelling of the gas dynamics in the chamber. The quality of the wafers for HEMT has been evaluated by fabricating 0.5 p~mgate length devices and good performances have been obtained with an f-r of 35 GHz and a noise figure of 1.1 dB at 12 GHz. One particularly impressive aspect of these wafers is their very low surface defect density of below 10 defects cm2. The record observed to date being 0.5 defects cm -2. Pseudomorphic GaInAs layers have also been grown exhibiting Hall mobilities of 6000 cm2/Vs at 300K with 2x1012 cm "2 sheet carrier concentration. A PMHEMT with 0.5 pm gate length has exhibited an fw of 50 GHz.
86 8.
J. Mun, A. Mbaye / ESPRIT H projects on compound semiconductors CONCLUSIONS
We have e x a m i n e d briefly the m a i n objectives of each E S P R I T II project on Compound Semiconductors and how they complement each other to m a k e up a strong overall p r o g r a m m e in the microelectronics sector. T h e r e is a large a m o u n t of results achieved by these projects, b u t with a limited space, we have choosen only some highlights for this paper. The p r o g r a m m e covers a wide range of very specialised technical areas which collectively, m a k e up the foundation of the III-V industry. It is difficult to envisage a single company alone having the resources to tackle all these areas. The synergy and the necessity of collaboration is therefore evident. 9.
REFERENCES
1990 A n n u a l Reports from projects 2035, 5003, 5013, 5018, 5035 a n d 5052.