SiNAPS Deliverable Report D4.5
WP4 (ver 1.1)
Grant agreement no: 257856
SiNAPS
Semiconducting Nanowire Platform for Autonomous Sensors
Collaborative Project
FP7-ICT-2009-5: Future and Emerging Technologies
“Towards Zero Power ICT” Proactive Scheme
Deliverable D4.5: Tests on miniaturised sensor
Due date of deliverable: Sept 30th 2013
Actual submission date: Jan 6th 2013
Start date of project: 01 Aug 2010
Duration: 39 months
Lead contractor for this deliverable:
Nanosens (Erik Puik)
Status: 1.1
Project co-funded by the European Commission within the 7th Framework Programme
(2007-2013)
Dissemination Level
PU
PP
RE
CO
Public
Restricted to other programme participants (including the Commission Services)
Restricted to a group specified by the consortium (including the Commission Services)
Confidential, only for members of the consortium (including the Commission Services)
1
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SiNAPS Deliverable Report D4.5
WP4 (ver 1.1)
1
Executive Summary (publishable) ............................................................. 3
2
Introduction (publishable) .......................................................................... 4
3
Integration for Issue 3 ................................................................................ 5
4
3.1
Module Miniaturisation ..................................................................... 5
3.2
Placement of the Dies ........................................................................ 6
3.3
Optimisations of the Thermoplastic Bonding Process ....................... 7
3.4
Final Devices after Die-bonding ........................................................ 7
Newly Developed Interconnection for Tests Issue 3 ................................. 8
4.1
5
6
7
Interfacing and Packaging.................................................................. 8
Testing the Series Arrangement of the Issue 3 PV Cells ........................... 9
5.1
Testing the Power Manager under Idealised Test Environments ...... 9
5.2
Tests of the Issue 3 Photovoltaic Module .......................................... 9
Testing the Issue 3 Pd Nanowire Die ....................................................... 10
6.1
General ............................................................................................. 10
6.2
Test Setup......................................................................................... 10
Wire Bond Tests ...................................................................................... 13
7.1
Wire Bonding the Nanowire Dies .................................................... 13
7.2
Wire Bonding the PV Cells.............................................................. 13
7.3
Wire Bonding the EPFL Power Dies ............................................... 13
7.4
Consequences for the Project ........................................................... 15
7.5
Further Actions Taken and Actions Still in Progress................Error!
Bookmark not defined.
8
Final Demonstrator Specifications ........................................................... 16
8.1
Specifications for Issue 2 & 3 .......................................................... 16
8.2
Settings for the Thermo Plastic Bonding Process ............................ 17
The information contained in this document is believed to be accurate at the time of publication. The authors do not assume
liability for any actions or losses arising from the use of the information contained in this document. The information contained in this
document supersedes that presented in any previous versions. This document must not be reproduced without the title page and
disclaimer intact, unless written permission to do so has been obtained from the authors.
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1 Executive Summary (publishable)
This report describes the integration & packaging concepts of the Issue 3 device
and the testing of the miniaturised sensor. It is referred in the project Description of
Work as deliverable 4.5 ‘Tests on miniaturised sensor’.
The report describes on the integration process of the final and smallest SiNAPS
device and the results of testing it.
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2 Introduction (publishable)
This is the report on deliverable D4.5: Tests on miniaturised sensor (Nanosens M38)
This report describes:
a. Integration for Issue 3
b. Newly Developed Interconnection for Testing Issue 3
c. Testing the Series Arrangement of the Issue 3 PV Cells
d. Testing the Issue 3 Pd Nanowire Die
e. Wire Bond Tests
f. Current, Alternative Actions for Wire Bonding the Issue 3 Device
g. Specifications of the Final SiNAPS Devices
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3 Integration for Issue 3
3.1 Module Miniaturisation
In the transition from Issue 3 to Issue 2, miniaturisation is the main challenge. The
reduction of projected area of the Issue 3 device is realised by applying smaller
components and further reducing the gaps between the components. The most
dominant determining factor for the size of the gap is the quality of the computervision-recognition of the edges of the parts. Chipped edges of the PV cells typically
vary from 20-50 microns; the power Die and the Pd sensor Die showed slightly less
chipped edges. The vision system, applied for recognition of the parts’ position has
the capability to average the chipped edges; by bringing the full optical contour of the
part in the computer vision equation, the optical sensor compensates anomalies at all
sides of the part.
This, however, only
operates well if the
illumination of the
computer
vision
system
is
symmetrical.
For
optimal result, a
fully symmetrical
(circular)
illumination
was
applied. In some
cases,
the
part
showed
asymmetrical chipping (picture right). By optimisations in the optical pattern
recognition algorithm, the effect could be suppressed for the larger part. The accuracy
of the position recognition system was between +/-10 microns (3 Sigma) for good
parts to +/- 25 micron for the most chipped parts. In combination with the applied
manipulator system, with an accuracy of +/-5 micron, a nominal placement gap of 50
micron could be realised.
In the transition from issue 2 to issue 3, the size of the power die was reduced from
1700x1700 micron to 1500x1500 micron. The PV cells were reduced from
1500x1000 micron to 800x500 micron. The Pd
sensor die was maintained at 1000x1000
micron.
The bonding scheme has been changed for the
new interconnection board as shown in the
figure. The interconnection has been
implemented diagonally to prevent too many
bonds of crossing over the dies. The long bonds
would make the devise extremely fragile. A
total number of 16 interconnections are
implemented of which 13 are indeed applied for
the basic functions of the device. The other
three are reserved for diagnosis.
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3.2 Placement of the Dies
Two substrate shapes were tested
for their quality to support the wire
bonding process. In the first
substrate version (figure right), the
contour of the effective area where
the dies are attached was milled
completely through the thickness
of the material, except for the four
corners that would keep that area
into position during assembly. The
substrate could be cut or forced out
by breaking the corners. In the
alternative version, the material
around the substrate contour was
milled away for 80% of the
material thickness, leaving 20% at
the bottom left after placement of
the dies. While this version was
designed to be provide better
stability during wire bonding,
cutting the substrate is more
difficult than the corners of the
first substrate version. While
performing the bond-tests, both
versions appeared to provide
sufficient stability during wire
bonding with no noticeable
difference. Therefore the first substrate version was selected for the final test batch.
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3.3 Optimisations of the Thermoplastic Bonding Process
The last period of the project has solely been focussing on the PET substrates since
the quality is superior to PS and the material is biodegradable. Over the last months,
the thermoplastic bonding process and related equipment is brought to a basic starting
level. The process has been characterised and tolerant working areas have been found
within the many parameters to vary.
3.4 Final Devices after Die-bonding
Changes to Issue 3 have led to the following geometrical changes in the transition
from Issue 2 and 3 (full updated specification in chapter 8):
Issue 2
Issue 3
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4 Newly Developed Interconnection for Tests Issue 3
4.1 Interfacing and Packaging
For the interconnection to the outside world, so far the Issue 1 Printed Circuit Board
was applied. However, this board has interconnected fingers at a pitch of 1,27mm,
which is not fine enough to fully interconnect all interconnects of the issue 3 device.
Therefore a higher resolution interconnection board was developed.
The
Issue 1 Board
has limited
resolution
which makes
the
interconnection
to the issue 3
device bulky
The solution for the
interconnection of
issue 3 is modular.
It uses a small
breakout board that
is interconnected to
a larger board to fit
the
standard
modular connector.
The larger board
may be integrated
with
the
radio
receiver and/or the battery. A small flexprint will be applied to connect the two
boards. The modular architecture enables cross testing in the evaluation phase.
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5 Testing the Series Arrangement of the Issue 3 PV
Cells
5.1 Testing the Power
Environments
Manager
under
Idealised
Test
The proposed energy harvester circuit, harvests energy from miniaturized solar cells
connected in series to charge the target NiMH battery. Functionality and efficiency
are described in a scientific paper ‘A Reconfigurable Micro Power Solar Energy
Harvester for Ultra-low Power Autonomous Microsystems’ by Naser Khosro Pour,
François Krummenacher and Maher Kayal.
The system was connected to the Issue 2 with the micro photovoltaic module from
IPHT and a rechargeable NiMH micro battery. Battery voltage was measured when
battery was discharged by a high discharge current, to estimate harvested solar
energy. Operating frequency and supply voltage of digital circuits and bias currents of
analogue circuits were reconfigured dynamically, based on measured battery voltage
to optimize power-performance of the microsystem.
The ambitious targets for size and power consumption were successfully realized. The
circuit occupied a core area of only 0.2mm2 in a 0.18μm CMOS process and features
a low power consumption of 390nW operating at its highest clock frequency.
5.2 Tests of the Issue 3 Photovoltaic Module
The first integrated photovoltaic module was tested at IPHT. Though assembly was
successfully performed on a batch of five systems, the surface of the PV cells
appeared not completely free from contamination, possibly the residue that was
applied for dicing the PV cells. This formed an obstacle for wire bonding the PV
cells. Cleaning was effective up to some point, that a single photovoltaic module
could be produced, however not without serious damage of the assembly; due to
rigorous cleaning and bonding attempts, the sensor and power Die were broken of the
substrate. Positive was that the module could be tested for output as shown in the
figure to the right.
The current-voltage characteristics were tested under AM1.5 illumination (black,
descending line). The power-voltage relation, as delivered by the module was
calculated (red line). Though the voltage of around 1.0 – 1.5V is still enough to
charge the NiMH micro battery (nominally 1.2V), the delivered output power was
significantly lower than the
best results achieved in earlier
tests. The low efficiency could
be explained by degradation
due to the extensive cleaning
and wire bonding operations
at the PV surface of the
module.
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6 Testing the Issue 3 Pd Nanowire Die
6.1 General
For these experiments a palladium nanowire chip was fabricated using Deposition and
Etching under an Angle (DEA). Two identical nanowires, with a width of 200nm, a
height of 20nm, and a length of 50µm were applied. These physical dimensions lead
to a wire resistance of approximately 8300Ω for each nanowire (293K, < 1ppm). The
tolerance on the resistance of the wires was less than 100Ω. The chip was wirebonded directly to an interface board for testing. The primary measurements were
done with a Keithley 2400 sourcemeter and initial measurements showed a resistance
of 8300Ω with a variation of approximately 12Ω ± 2Ω at a hydrogen concentration of
900ppm. The error in measurement is due to wire resistance and cable noise in the
connection from the sourcemeter to the nanowires.
6.2 Test Setup
The Sensor Die was put on a printed
circuit board to provide the bias currents
for the nanowires. On this board also a
temperature and humidity sensor were
integrated
for
compensation
of
environmental quantities. For these
measurements, the humidity sensor was
not yet used. This temperature sensor is
further referred to as the nearbytemperature-sensor.
The SiNAPS sensor Die and PCB were
placed into a test chamber in which the
environmental state can be varied. An
internal fan in the test chamber takes care
for circulation of the test gasses.
Temperature is controlled within +/- 0,1K
by a Peltier-element. Test gases, in this
case Hydrogen, can be inserted into the
chamber; the chamber can also be flushed with environmental air or Nitrogen.
Due to the nature of the nanowire, the wire resistance not only changes due to
hydrogen absorption, it also changes due to thermal expansion of the wire itself.
Therefore, accurate hydrogen sensing with the SiNAPS Die cannot be done without a
temperature compensation arrangement. Although this is accounted for in the
power/ADC die designed, tested and fabricated by EPFL, in this setup it was
implemented using a drop forge technique to cover one of the two identical nanowires
with a low-permeable H2 coating consisting of a UV curable polymer. This is referred
to as the secondary nanowire, the uncoated nanowire being primary. The semicrystalline coating on the secondary nanowire acts as a passivation layer and hinders
hydrogen from reaching the wire itself. Due to the low E-modulus of the coating
material, the compound remains flexible to allow the wire to expand and recover by
the influence of temperature changes. In time, but with a considerably higher time
constant, hydrogen will reach the secondary wire causing it to respond to the diffusion
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of hydrogen in the palladium wire. Before this process takes place however, the
secondary nanowire can be applied as an adequate temperature reference for the
primary nanowire, responding to temperature changes in the exact same manner and
as such enabling accurate temperature compensation. Temperature measurements
with the nearby temperature sensor were performed for verification of the temperature
compensation mechanism.
It is anticipated that the temperature response time-constant of the nearby temperature
sensor will differ significantly from the time-constant of the secondary nanowire. This
was tested by exposing the sensor to a
predefined temperature fluctuation
sequence in the test chamber. The
temperature sequence had a sine
profile with a maximum of 28.0°C and
a minimum of 20.0°C. The sine profile
was chosen to ensure a good mixture
both the presence of between faster
and slower temperature transients. The
wire was responding to the
temperature change as seen in upper
chart of the figure left. Plotted are the
nanowire
response
and
the
temperature of the chamber (middle
curve, scale to the right). As can be
seen in the chart, the output of the
primary nanowire shows a strong
positive
correlation
with
the
temperature change. At this time scale,
the permeability of the coating, and
the obstruction of changes in wire
shape may be considered to be
minimal, since influences of these
parameters would inevitably lead to
distortions in the correlation between
the primary and the secondary wire. First indications of the correlation between the
temperature of the chamber and the nearby-temperature-sensor seem good as well, but
more investigations are needed to understand the behaviour at higher gradients of
temperature change. The lower part of the figure shows the compensated output of the
primary nanowire. In this first test, no hydrogen was inserted in the test chamber yet,
so the output should be steady. The measurement confirms this expectation; note that
the scale of the lower graph has been expanded by a factor 150.
At this time initial tests with inserting hydrogen in the test chamber show sufficient
response of the primary nanowire and a delayed response of the secondary nanowire.
An algorithm is under development to apply the nearby-temperature-sensor and the
primary nanowire output to optimize the accuracy of the system at the dynamics of
realistic environments, from almost steady to rapidly changing.
Given the tests so far, hydrogen sensing with the new Pd Die has proven its value in
low power sensing applications for Hydrogen. Work on the compensation algorithms
is in progress. Given the relatively cow manufacturing costs character of the hydrogen
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Die, application in low cost applications for Green houses or applications in the
Hydrogen economy seems feasible.
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7 Wire Bond Tests
7.1 Wire Bonding the Nanowire Dies
The Nanosens Pd nanowire Die were equipped with
standard bond pads of 100 x 100 Microns. This had been
a design consideration to enable straightforward wire
bonding technique with Al or AU wire. Wire bonding of
the sensor Die can be successfully done at Nanosens or
IPHT (see picture right).
7.2 Wire Bonding the PV Cells
Bonding the PV cells is done by applying a very soft and rather thick (30 micron) Al
wire, a connection is made by pressing the Aluminium in the pores of the material. In
this way an adhesive bond can be made. As quite some energy is needed to bring the
materials into contact with each other, this process is an intrinsic risk for the
thermoplastic bonded Dies, the amount of energy introduced in the Die could lead to
de-bonding. As was tested in Period 2, this was the main reason to switch to PET as
substrate material; bonding strengths on PET appeared
superior. PS for the substrate material was dropped.
The bonding process was tested on the issue 2 power
demonstrator. Wire bonding on the PV cells could be
performed successfully (figure right). Wire bonding
improved after cleaning with acetone-IPA and increasing
the power settings.
Unfortunately, the first batch of Issue 3 devices showed
residue on the surface of the PV Dies, most likely a result of imperfect cleaning
before assembly. One Issue 3 photovoltaic module could be rescued and tested. In this
module the power module and the sensor module were lost. By numerous wire
bonding attempts, the sensor Die was de-bonded from the substrate. The power Die
however was broken from the substrate, leaving a part of the Si on the substrate. In
this drawback also has a positive tiding; the bonding strength on the PET substrate has
been exceptionally well for this particular Die.
The process of wire bonding the PV cells is not an industrially applicable process
since no metallic layer is applied on the PV Dies. This was discussed in the project
and accepted since it is sufficient for the proof-of-principle demonstration. Equipping
the PV Cells with a partial metallic layer would draw serious resources from the
project focus of developing better PV cells.
7.3 Wire Bonding the EPFL Power Dies
The EPFL Dies are produced with a standard 0.18 micron CMOS process. CMOS
processes virtually always apply Aluminium bond pads. The size of the bond pads of
60 x 60 micron, with a pitch of 90 microns, called an ‘ultra fine pitch application’
however is not a usual industrial process. This has lead to considerable delay in the
project.
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The first attempt to wire bond the power die was at
Nanosens, but their wire bonder appeared not accurate
enough for the 60 micron positioning spec. The second
attempt was at IPHT, and though their bonder setup was
able to position the bond position well, bond did not stay
within the 60 micron square.
An alternate solution was found in a gold ball bonding
process at TNO Science & Industry in the Netherlands.
The ball bonding process could be performed smoothly without damaging the
substrate or the Dies. Good bond could be produced. Unfortunately this path was
delayed as well due to the 90 micron pitches of the bond pads. The diameter of the
wire-bonding tool appeared too large for neighbouring bonds (figure below).
The picture shows gold ball bonds with a base that just fits on the bond pads of the
EPFL Die. In the circle however, a bond was made earlier. Due to the diameter of the
bond tool it has been ‘bumped’ off of the Die surface leaving a thorn off weld at the
surface (matte area).
Analysis of the problem learned that the tip-shape of the applied
bonding tool was indeed too wide for the required ultrafine
bonding application. This is determined by the applied bonding
‘wedge or capillary’ (picture). The capillary is a little ceramic
tube with a cavity inside for the ball to be squeezed. The ball is
formed by applying electrical current to the wire of the tip. After
this, the ball is squeezed to the surface with an applied force and
ultrasonic vibrations to melt the surface and weld it to the bond
pad. As shown in the picture (right), the ball is shaped with
diameter “b” and the wall of the tip “a” is the minimal distance
between two neighbouring balls. The sum of a & b should be less
than 90 microns.
To solve the problem, a new smaller tip was acquired with dimensions a=38 and b=50
micron. Together with a thinner wire of 17.5 microns a bond pitch of 90 micron
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should be feasible. Unfortunately, the new combination of wedge and wire was not
yet successful due an incompatibility between the diameter of the wire and the hole in
the capillary. Recent investigations have learned that the bonding capillary has not
been produced well or was damaged during assembly in the wire bonder. The supplier
is invited to discuss this problem.
7.4 Consequences on the deliverables of the project the
Project
The difficulties, with wire bonding the issue 3 device, prevent the final demonstrators
to be tested. However, it concerns only the test of the integrated devices, all
functionality of the device has been tested on macro scale:
 The PV-cells have been tested in conjunction of the power die by EPFL (D3.2);
 The sensor, being a resistive device, was emulated on the bench at EPFL by
substituting it with a potentiometer. This way of substitution is a proven way of
testing read-out electronics at Nanosens. The EPFL die was performing according
to specification (D3.4);
 Output of the PV cells has been tested by IPHT (D1.4);
 Integration of Issue 2 has been successfully tested and described in D4.4;
 Successful readout of the new Pd sensor Die has been reported in this deliverable
(D4.5);
 Integration of the thermoplastic bonding process and high-density assembly for
Issue 3 has been described in this deliverable (D4.5).
Given the successes of functional testing for the PV cells, Power die, sensor die and
the high bonding pitch it may be concluded that the SiNAPS project is a success and
that a small sensor system as specified (4mm3) can be realized. Detailed performance
of the system will be subject of further investigation but is not within the scope of the
project.
With the completion of this last project deliverable the project can be ended.
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8 Final Demonstrator Specifications
8.1 Specifications for Issue 2 & 3
Quantity
Issue 2
Issue 3
Dimensions in x-y plane [um]
(+/-50 unless stated otherwise)
- External Substrate
5000 x 5000
2870 x 2870
- Effective Device
4300 x 3300
2530 x 2530
- PV Cell
1500 x 1000
1000 x 500
- Power Die
1700 x 1700
1525 x 1525
- Sensor
1000 x 1000
1000 x 1000
- Gap size
100
50
Dimensions Thickness [um]
(+/-25 unless stated otherwise)
- Substrate
1000 +/-50
1000 +/-50
- PV Cell
700
700
- Power Die
300
300
- Sensor
400
400
Device Area [mm2]
(+/-0,25)
- Substrate
25,00
8,24
- Device Area
14,19
6,40
Device Volume [mm3]
(+/-1,5)
(Bond Wire Height 0,200)
- Including Substrate
47,50
15,66
- Without Substrate
26,96
12,16
Specifications of electronics circuit for Issue 2 & Issue 3
Technology
Europractice UMC180nm
Active die area
670 X 370 µm2
Chip Area, including pads
1525X1525µm2
Pad Size
69 X 69 µm2
Pad-to-Pad distance
99 µm
Specifications of Varta V6HR as energy storage option
Technology
NiMH battery
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Nominal Operating Voltage
1.2V
Size
D: 6.8mm, H: 2.15mm
Energy Capacity
6,200 µAh
Peak Discharge Current
18mA
Cycle life
1,000
Specifications of TZ1053 as external wireless transceiver
Supply Voltage
1-1.5V (NiMH-compatible)
Size
5x5mm2
Current consumption during data
transmission
3mA
Current consumption during data
reception
2.8mA
Current consumption during standby
time
5µA
8.2 Settings for the Thermo Plastic Bonding Process
A good working area is found with the following settings (for PET)
Tolerances are applied within +/- 10%, except placement height +/- 0,1 mm
Temperature
325
°C
Speed
2
mm/s
Placement height z
-93.58
EPFL-module in mm
-93.42
Pd-sensor in mm
-93.10
PV-cell in mm
Mate time
0.75
s
Release time
0.10
s
Release distance Z
10
mm
Placement Force
35.70
gram
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