An integrated circuit (IC) chip with a self-contained fluid sensor and method of making the chip. The sensor is in a conduit formed between a semiconductor substrate and a non-conductive cap with fluid entry and exit points through the cap. The conduit may be entirely in the cap, in the substrate or in both. The conduit includes encased temperature sensors at both ends and a central encased heater. The temperature sensors may each include multiple encased diodes and the heater may include multiple encased resistors

Balvin, Manuel A.

Callahan, Michael P.

Manos, George

NASA Technical Reports Server

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(12) United States Patent
Manos et al.
(54) INTEGRATED CIRCUIT (IC) CHIP WITH A
SELF-CONTAINED FLUID SENSOR AND
METHOD OF MAKING THE CHIP
(71) Applicant: U.S.A. as represented by the
Administrator of the National
Aeronautics and Space
Administration, Washington, DC (US)
(72) Inventors: George Manos, Laurel, MD (US);
Manuel A. Balvin, Springfield, VA
(US); Michael P. Callahan, Boise, ID
(US)
(73) Assignee: The United States of America as
represented by the Administrator of
NASA, Washington, DC (US)
(*) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by 50 days.
(21) Appl. No.: 15/278,359
(22) Filed: Sep. 28, 2016
(65) Prior Publication Data
US 2018/0086629 Al Mar. 29, 2018
(51) Int. Cl.
GOLF 1/708 (2006.01)
GOIK 7/01 (2006.01)
B81B 7/00 (2006.01)
B81C 1/00 (2006.01)
GOLF 11684 (2006.01)
(52) U.S. Cl.
CPC ........ B81B 7/0061 (2013.01); B81C 1/00309
(2013.01); GOLF 1/7084 (2013.01); GOIK
(io) Patent No.: US 10,189,700 B2
(45) Date of Patent: Jan. 29, 2019
7/01 (2013.01); B81B 220110278 (2013.01);
GOLF 116845 (2013.01)
(58) Field of Classification Search
CPC ......... 138113 7/00; 138113 7/006; 138113 7/0061;
B81C 1/00; B81C 1/003; B81C 1/003;
B81C 1/00309; GO1F 1/70; GO1F 1/78;
GO1F 1/7084
USPC .......................................................... 257/467
See application file for complete search history.
(56) References Cited
U.S. PATENT DOCUMENTS
7,181,963 B2 * 2/2007 Bork ......................... GOIF 1/68
73/204.26
7,259,080 B2 * 8/2007 Quenzer et al. ........ HOIL 21/46
438/455
* cited by examiner
Primary Examiner Monica D Harrison
(74) Attorney, Agent, or Firm Christopher O. Edwards;
Bryan A. Geurts; Mark P. Dvorscak
(57) ABSTRACT
An integrated circuit (IC) chip with a self-contained fluid
sensor and method of making the chip. The sensor is in a
conduit formed between a semiconductor substrate and a
non-conductive cap with fluid entry and exit points through
the cap. The conduit may be entirely in the cap, in the
substrate or in both. The conduit includes encased tempera-
ture sensors at both ends and a central encased heater. The
temperature sensors may each include multiple encased
diodes and the heater may include multiple encased resis-
tors.
3
148-
3
00
5 Claims, 5 Drawing Sheets
160
https://ntrs.nasa.gov/search.jsp?R=20190000793 2019-08-30T09:53:41+00:00Z
U.S. Patent Jan. 29, 2019
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U.S. Patent Jan. 29, 2019 Sheet 3 of 5 US 10,189,700 B2
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U.S. Patent Jan. 29, 2019 Sheet 5 of 5 US 10,189,700 B2
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US 10,189,700 B2
INTEGRATED CIRCUIT (IC) CHIP WITH A
SELF-CONTAINED FLUID SENSOR AND
METHOD OF MAKING THE CHIP
ORIGIN OF THE INVENTION
The invention described herein was made by an employee
of the United States Government, and may be manufactured
and used by or for the Government for governmental pur-
poses without the payment of any royalties thereon or
therefor.
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention is generally related to instruments
for measuring fluid temperature and flow rate and more
particularly to sensors for space-bourne applications for
measuring fluid temperature and flow rate.
Background Description
National Aeronautics and Space Administration (NASA)
scientists are developing next generation microfluidic instru-
ments, e.g., lab-on-a-chip, for space based applications and
on planetary bodies. Producing a lab-on-a-chip requires
advancements in miniaturization, especially for analytical
systems, requires an on-chip, in situ fluid flow and fluid
temperature measurement capability. Unfortunately, state of
the art sensors are either too large for integration on-chip,
requiring diverting fluid off-chip for measurement by a flow
sensor and a temperature sensor. Only after the measurement
is complete is the fluid returned to the chip. These sensors
are still incapable of measuring flow rates, while requiring
increased fluid volume (and corresponding weight) at a
higher risk of on-board system fluid leaks.
Thus, there is a need for an on-chip flow and temperature
sensor for measuring microfluidic flow rates and tempera-
tures, and more particularly, for accurately measuring micro-
fluidic flow rates and temperatures for next generation
microfluidic space-bourne instruments traveling to extrater-
restrial planetary bodies.
SUMMARY OF THE INVENTION
An aspect of the invention is a self-contained fluid flow
rate and temperature sensor;
Another aspect of the invention is an on-chip capability
for measuring nano-liter per minute fluid flow rates over a
broad temperature range;
It is yet another aspect of the invention an on-chip,
self-contained fluid flow rate and temperature sensor for
measuring fluid flow at rates in the nano-liter per minute
range and over temperatures ranging from below —80° C. to
above 150° C. in any application that requires accurate
temperature and flow measurements.
The present invention relates to an integrated circuit (IC)
chip with a self-contained fluid sensor and method of
making the chip. The sensor is in a conduit formed between
a semiconductor substrate and a non-conductive cap with
fluid entry and exit points through the cap. The conduit may
be entirely in the cap, in the substrate or in both. The conduit
includes encased temperature sensors at both ends and a
central encased heater. The temperature sensors may each
include multiple encased diodes and the heater may include
multiple encased resistors.
2
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, aspects and advantages
will be better understood from the following detailed
5 description of a preferred embodiment of the invention with
reference to the drawings, in which:
FIGS. 1A-B show a schematic and plan view example of
a Dynamic On-Chip Flow and Temperature Sensor (DOC-
F1aTS) for sensing on-chip fluid flow and temperature,
10 according to a preferred embodiment of the present inven-
tion;
FIG. 2 shows a flow diagram for fabricating the sensors
on a semiconductor wafer;
FIGS. 3A-G show a cross-sectional example of forming
15 an IC chip with a preferred flow and temperature sensor;
FIG. 4 shows an alternate embodiment cross-sectional
example of forming an IC chip with a preferred flow and
temperature sensor.
20 DESCRIPTION OF PREFERRED
EMBODIMENTS
Turning now to the drawings, and more particularly,
FIGS. 1A-B show a schematic and plan view example of a
25 Dynamic On-Chip Flow and Temperature Sensor (DOC-
F1aTS) 100 for sensing on-chip fluid flow and temperature,
according to a preferred embodiment of the present inven-
tion. Preferred sensors 100 provide on-board, on-chip capa-
bility for measuring flow rates in the nano-liter per minute
30 (nl/min) range, at temperatures from below —80° C. to above
150° C. in any application that requires accurate temperature
and flow measurements.
Fluid enters 102 at one end of an embedded conduit 104
where one or more front-end or input temperature sensors
35 106 measure fluid temperature. One or more heating ele-
ments 108 selectively heat the fluid before it passes by one
or more back-end or output temperature sensors 110 to exit
112 the conduit 104. Preferably, the channel 102 is formed
partially in, or on, a capped semiconductor, e.g., silicon (Si),
40 wafer 114. Preferably also, temperature sensors 106,110 and
heater 108 are encased in Silicon Nitride (SiN) for electrical
isolation, and are connected through wires 116 externally at
pads 118. For maximum fluid surface contact, preferably, the
temperature sensors 106, 110 are suspended in the conduit
45 104 to optimize sensitivity and response time.
In this example the input temperature sensors 106 and
output temperature sensors 110 each include two pair, or 4,
polysilicon diodes, i.e., PN junctions 106P, 106N and 110P,
10N. Also in this example, the heaters 108 are a pair of
50 polysilicon resistors (R) 108R with resistor current 0'.)
selectively applied to dissipate power (1,2R) generating
localized heat in the conduit 104. The polysilicon diodes
106P, 106N and 110P, 11ON exhibit determinable sensitivity
to junction temperature (T). Diode 106P, 106N and 110P,
55 11ON junction thermal voltage (VT) is a constant at any
absolute temperature, defined by VT kTq, where k is the
Boltzmann constant, q is the magnitude of charge of an
electron, and the rate of change is —2.2 mi11iVolts (-2.2 mV)
per degree Kelvin (° K.).
60 Fluid entering 102 the conduit 104 at input temperature
sensors 106 exhibits a temperature difference (dT) with the
fluid exiting 112 at output temperature sensors 110, that may
also be measured among individual sensor junctions 106P,
106N and 110P, llON. That temperature difference is depen-
65 dent upon the length of time passing heaters 108 and
between sensors 106, 110, and, therefore, is a measure of
fluid flow or velocity through the conduit 104. During
US 10,189,700 B2
3
operation, temperature sensors 106, for example, 110 may
be biased at a fixed current (ID) or fixed voltage (VD) and
absolute temperature (T) for each diode may be derived
from the well-known, ideal diode relationship,
5
/ VD
ID = lslenv, — 1),
where n is a diode quality factor. 10
Thus, the front-end temperature sensors 106 allow for one
or more initial fluid temperature readings before passing the
heater 108. Fluid thermal conductance, fluid heat capacity
combine with heat from power to the heaters 108 to elevate 15
temperature of the fluid traversing the conduit 104. The
back-end temperature sensors 110 allow for measuring heat
injected into the conduit 104 fluid from dT. For example, the
temperature difference reflected in diode voltage change
(dVD) between sensor junctions 106P, 106N and 110P, 11ON 20
provides a measure of microfluidic flow rate through the
conduit 104 according to the relationship, dVD/dT=VD/T—
Eg/T-2Kq, where Eg is the substrate energy band gap.
Accordingly, a self-contained preferred sensor 100 provides
a single chip solution for accurately measuring microfluidic, 25
on-chip flow rates and temperatures, especially for next
generation microfluidic space-bourne instruments.
FIG. 2 shows a flow diagram 120 example of fabricating
the preferred sensors (100 in FIGS. 1A-B) on a semicon-
ductor substrate wafer 114. First in this example, micro- 30
channels 104 are etched 122 into the wafer. A sacrificial
layer is deposited 124 on to the wafer to back fill the
substrate channels 104 and re-planarize to the wafer surface.
A lower encasement layer is formed 126 on the wafer, e.g.,
using low pressure chemical vapor deposition (LPCVD). 35
Polysilicon, doped or undoped, is deposited 128 on the
lower encasement layer, patterned and selectively doped, to
define 130 the temperature sensors 106, 110, e.g., diodes,
and resistive heater(s)108. Connective wiring is formed 132
to each of the temperature sensor 106, 110 diodes and the 40
resistive heater(s) 108. Forming 134 an upper encasement
layer on the patterned polysilicon, encases and encloses all
temperature sensors 106, 110 and heaters 108. Pads for
probing or connecting to other sensing circuits are formed
136, e.g., at the edge of the sensor 100, wafer 114 or each 45
chip, and wafer and/or chip fabrication may complete. A
corresponding micro-channel in a non-conductive cap, e.g.,
pyrex, bonded 138 to the wafer 114 forms/completes the
conduit 104.
FIGS. 3A-G show a cross-sectional example of forming 50
an IC chip with a preferred flow and temperature sensor 100
through 3-3 in FIG. 113, formed as described in FIG. 2 and
with like features labeled identically. Although the channel
140 jn silicon wafer 114 shown in this example has a
rectangular cross-section with rounded corners, this is for 55
example only. The channel 140 may have any shape as
desired formed in the substrate 114, e.g., completely
rounded or cylindrical, oval or square, as selected by design
and constrained by fabrication.
Typically, a preferred sensor 100 occupies a small portion 60
of the overall integrated circuit (IC) chip. For a 10 mmx15
mm chip, for example, the flow and temperature sensor 100
may be 0.08 mmx0.8 mm within a 10.0 mm long by 0.08
mm wide channel 140 etched 122 in the semiconductor
wafer 114. A Low Thermal Oxide (LTO) may be deposited 65
124 to form sacrificial material, back filling the channels
140, e.g., using LPCVD. Then, sacrificial material is
_►,
removed from the wafer, e.g., using a typical chemical-
mechanical (chem-mech) polish, to re-planarize the wafer
surface, with the back fill LPCVD LTO 142 remaining in the
channel(s) 104 and providing a flat surface for subsequent
fabrication.
Having filled and re-planarized, LPCVD SiN layer forms
126 the lower encasement layer 144. The lower encasement
layer 144 is 100-200 nanometers thick (100-200 nun), pref-
erably, 150 nm thick. The lower encasement layer 144 is
patterned, e.g., using a typical photolithographic pattern
(mask) and etching, to define sensor 106, 110 locations and
heater 108 locations. The patterned lower encasement layer
144 positions the temperature sensor 106, 110 diodes and
resistive heaters 108 in the conduit 104, e.g., centrally
located, for maximum fluid surface contact in the conduit
104.
Eighty micron (80 µm) long polysilicon strips, preferably,
0.2 µm thick and 0.5-1.0 µm wide, are formed using a
LPCVD and mask and etch. The polysilicon strips locate the
temperature sensor 106, 110 diodes and heater resistors
108R. For example, a 0.2 µm thick polysilicon layer may be
deposited as doped polysilicon, e.g., P-doped, undoped, or
intrinsic polysilicon. Patterning the polysilicon defines the
strips, and doping the strips defines diodes and heaters. For
undoped polysilicon, for example, the strips may be
implanted with P-type dopant, preferably, boron. Masking
the P-doped polysilicon to protect the resistors 108R and
portions of the diode strips 146P, exposed portions 146N of
the strips are implanted with N-type dopant, preferably,
phosphorus, forming polysilicon diodes 146.
After forming 132 connective wires 116 to each of the
temperature sensor 106, 110 diodes and the resistive
heater(s) 108, an upper encasement layer 148 is deposited.
Preferably, the upper encasement layer 148 is SiN, 50-150
nun, and preferably, 150 nm thick. Then, the upper encase-
ment layer 148 is patterned 134, encasing and enclosing all
polysilicon temperature sensors 106, 110 and heaters 108 in
a silicon nitride membrane strong enough to withstand the
laminar flow within the conduit 104. Other IC circuits, e.g.,
sensing and support circuits, may be formed tailored by
design to the preferred sensors 100. Bond pads may be
formed 136, for example, by depositing and patterning a
suitable metal with the bond pads 118 remaining exposed.
The bond pads 118 provide, for example, for connection to
another chip, for wafer level test probing, or for connection
to other sensing circuits, e.g., at the edge of the sensor.
In this example IC fabrication completes 138 connecting
circuits together, to bond pads 118 and off chip, and the
remaining LPCVD LTO 140' is removed suspending the
temperature sensors 106, 110 and heaters 108 in the middle
of the conduit 104. In operation the suspended temperature
sensors 106, 110 are completely immersed in the fluid in the
conduit 104, thermally isolating them from ambient for
faster flow and temperature change responses.
After completing ICs 138, bonding a corresponding chan-
nel 150 in a pyrex cap 152 to the wafer 114 completes the
conduit 104. The bonded pyrex cap 152 houses the flow and
temperature sensors in the completed conduit 104. The
pyrex cap 152 also houses a tapered inlet via 102 and outlet
via 112 clamped to the wafer 114 witr nano-ferrules and
capillary tubes (not shown) to produce a leak-tight channel
to macro-scale connection.
FIG. 4 shows an alternate embodiment cross-sectional
example of forming an IC chip with a preferred flow and
temperature sensor 160, also formed as described in FIG. 2
and with like features labeled identically. In this alternate
example channels are not formed in the wafer 114. Instead,
US 10,189,700 B2
5
the lower encasement layer 144 is formed on the semicon-
ductor wafer 114, placing the sensors 162 and heaters at the
bottom of the conduit 104'. The upper encasement layer 148
encases and encloses all polysilicon sensor diodes 162 and
heaters. Also in this example, the channel 150 in the pyrex
cap 152 bonded to the wafer 114 forms the entire sensor
conduit 104. While this embodiment is less thermally iso-
lated, on the bottom on the conduit 104, the temperature
sensors 106, 110 and heaters 108 are more mechanically
robust and simpler to fabricate.
Advantageously, preferred on-chip flow and temperature
sensors eliminate the need to route fluid off-chip and out of
an analytical system for separately measuring flow rate and
temperature. Preferred sensors are capable of accurately
measuring flow rates down to the nano-liter per minute
range. Temperature measurement capabilities range from
below —80° C. to above 150° C. Further, preferred sensors
provide for analyzing relatively small, even minute, indi-
vidual system samples, thereby reducing the total required
fluid mass and volume. This reduction is a key requirement
for space-bourne microfluidic instruments used on both
space and planetary platforms. Thus, preferred sensors pro-
vide an on-board, on-chip application capability wherever
accurate temperature and flow measurements may be
required.
While the invention has been described in terms of
preferred embodiments, those skilled in the art will recog-
nize that the invention can be practiced with modification
within the spirit and scope of the appended claims. It is
intended that all such variations and modifications fall
within the scope of the appended claims. Examples and
drawings are, accordingly, to be regarded as illustrative
rather than restrictive.
6
What is claimed is:
1. An integrated circuit (IC) chip including a self-con-
tained fluid sensor comprising:
a semiconductor substrate;
5 a non-conductive cap disposed on said semiconductor
substrate;
a conduit at the interface between said semiconductor
substrate and said nonconductive cap, each end of said
conduit passing through said non-conductive cap;
10 
a temperature sensor in said conduit at said each end; and
a heating element in said conduit between the temperature
sensors wherein the temperature sensors and said heat-
ing element are encased in dielectric; further wherein
said non-conductive cap is a pyrex cap with a channel
at said semiconductor substrate, wherein said conduit
15 comprises said channel and
wherein said semiconductor substrate comprises a mirco-
channel, said conduit further comprises said mirco-
channel, the encased temperature sensors and said
heating element being suspended in said conduit at said
20 interface.
2. An IC chip as in claim 1, wherein the encased tem-
perature sensors and the encased heating element are dis-
posed on said semiconductor substrate at said interface.
3. An IC chip as in claim 1, wherein said semiconductor
25 substrate is silicon and each said temperature sensor com-
prises one or more polysilicon diodes and said heating
element comprises one or more polysilicon resistor.
4. An IC chip as in claim 3, wherein said one or more
polysilicon diodes comprises two pair of diodes and said
30 polysilicon resistor comprises a pair of resistors.
5. An IC chip as in claim 4, further including one or more
circuits on said silicon substrate and connected to said two
pair of diodes and said pair of resistors.


Integrated Circuit (IC) Chip with a Self-Contained Fluid Sensor and Method of Making the Chip

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